Drop requirement for CLA in contribution.md

It is no longer necessary for contributors to send a CLA to ARM
before making contributions. Contributors must instead add a
"Signed-off-by:" line to each commit, which certifies that the
contribution is made under the Developer Certificate of Origin
(DCO).

Update contributing.md to reflect this new policy and add a copy of
the DCO to the repository.

Change-Id: I7ca98bffc3bf57e8bdd51d763c24f13e415a328b
Signed-off-by: Dan Handley <dan.handley@arm.com>

contributing.md

 Contributing to ARM Trusted Firmware
 ====================================
 
-Before you start contributing to this project you must sign the ARM
-Contributor License Agreement (CLA).
-
-Individuals who want to contribute their own work must sign and return an
-Individual CLA. Companies that want to contribute must sign and return a
-Corporate CLA if their employees' intellectual property has been assigned to
-the employer. Copies of the CLAs are available from the [contributing page] of
-the ARM website. Please wait for ARM to confirm acceptance of your CLA before
-making contributions.
-
-For this project, ARM also requires the GitHub account name(s) associated with
-each individual contributor or the designated employees of corporate
-contributors. Only contributions originating from these accounts will be
-considered covered by the CLA. To avoid delay, you should provide the Github
-account name(s) at the same time as the signed CLA.
-
-ARM reserves the right to not accept a contribution. This may be for technical,
-commercial or legal reasons.
-
-
 Getting Started
 ---------------
 
@@ -77,7 +57,12 @@ Making Changes
 Submitting Changes
 ------------------
 
-*   Ensure ARM has your signed CLA and has confirmed acceptance of it.
+*   Ensure that each commit in the series has at least one `Signed-off-by:`
+    line, using your real name and email address. The names in the
+    `Signed-off-by:` and `Author:` lines must match. If anyone else contributes
+    to the commit, they must also add their own `Signed-off-by:` line.
+    By adding this line the contributor certifies the contribution is made under
+    the terms of the [Developer Certificate of Origin (DCO)][DCO].
 *   Push your local changes to your fork of the repository.
 *   Submit a [pull request] to the [arm-trusted-firmware] `integration` branch.
     *   The changes in the [pull request] will then undergo further review and
@@ -101,7 +86,7 @@ Submitting Changes
 
 - - - - - - - - - - - - - - - - - - - - - - - - - -
 
-_Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved._
+_Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved._
 
 
 [User Guide]:                           ./docs/user-guide.md
@@ -109,8 +94,8 @@ _Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved._
 [Porting Guide]:                        ./docs/porting-guide.md
 [Firmware Design]:                      ./docs/firmware-design.md
 [Acknowledgements]:                     ./acknowledgements.md "Contributor acknowledgements"
+[DCO]:                                  ./dco.txt
 
-[contributing page]:            http://www.arm.com/community/open-source-contributing.php
 [GitHub account]:               https://github.com/signup/free
 [Fork]:                         https://help.github.com/articles/fork-a-repo
 [issue tracking repository]:    https://github.com/ARM-software/tf-issues

dco.txt

+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+1 Letterman Drive
+Suite D4700
+San Francisco, CA, 94129
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+    of my knowledge, is covered under an appropriate open source
+    license and I have the right under that license to submit that
+    work with modifications, whether created in whole or in part
+    by me, under the same open source license (unless I am
+    permitted to submit under a different license), as indicated
+    in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including all
+    personal information I submit with it, including my sign-off) is
+    maintained indefinitely and may be redistributed consistent with
+    this project or the open source license(s) involved.