doc: Add minimal Sphinx support

Add the essentials for supporting a Sphinx documentation build:

- A makefile under docs/ to invoke Sphinx with the desired output
  format
- A Sphinx master configuration file (conf.py)
- A single, top-level index page (index.rst)
- The TF.org logo that is integrated in the the sidebar of the
  rendered output

Change-Id: I85e67e939658638337ca7972936a354878083a25
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

docs/Makefile

+#
+# Copyright (c) 2019, ARM Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+# Minimal makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line.
+SPHINXOPTS    =
+SPHINXBUILD   = sphinx-build
+SPHINXPROJ    = TrustedFirmware-A
+SOURCEDIR     = .
+BUILDDIR      = build
+
+# Put it first so that "make" without argument is like "make help".
+help:
+	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+.PHONY: help Makefile
+
+# Catch-all target: route all unknown targets to Sphinx using the new
+# "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
+%: Makefile
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)

docs/conf.py

+# -*- coding: utf-8 -*-
+#
+# Copyright (c) 2019, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+#
+# Configuration file for the Sphinx documentation builder.
+#
+# See the options documentation at http://www.sphinx-doc.org/en/master/config
+
+# -- Project information -----------------------------------------------------
+
+project = 'Trusted Firmware-A'
+
+version = '2.1'
+release = version # We don't need these to be distinct
+
+
+# -- General configuration ---------------------------------------------------
+
+# Add any Sphinx extension module names here, as strings. They can be
+# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
+# ones.
+extensions = []
+
+# Add any paths that contain templates here, relative to this directory.
+templates_path = ['_templates']
+
+# The suffix(es) of source filenames.
+source_suffix = '.rst'
+
+# The master toctree document.
+master_doc = 'index'
+
+# The language for content autogenerated by Sphinx. Refer to documentation
+# for a list of supported languages.
+#
+# This is also used if you do content translation via gettext catalogs.
+# Usually you set "language" from the command line for these cases.
+language = None
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+# This pattern also affects html_static_path and html_extra_path .
+exclude_patterns = []
+
+# The name of the Pygments (syntax highlighting) style to use.
+pygments_style = 'sphinx'
+
+
+# -- Options for HTML output -------------------------------------------------
+
+# Don't show the "Built with Sphinx" footer
+html_show_sphinx = False
+
+# Don't show copyright info in the footer (we have this content in the page)
+html_show_copyright = False
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+html_theme = "sphinx_rtd_theme"
+
+# The logo to display in the sidebar
+html_logo = 'resources/TrustedFirmware-Logo_standard-white.png'
+
+# Options for the "sphinx-rtd-theme" theme
+html_theme_options = {
+    'collapse_navigation': False, # Can expand and collapse sidebar entries
+    'prev_next_buttons_location': 'both', # Top and bottom of the page
+    'style_external_links': True # Display an icon next to external links
+}

docs/index.rst

+Arm Trusted Firmware-A Documentation Index
+==========================================
+
+.. toctree::
+   :maxdepth: 1
+   :caption: Design Documents
+
+   arm-sip-service
+   auth-framework
+
+   .. toctree::
+   :maxdepth: 1
+   :caption: Release Notes
+   change-log
+
+   .. toctree::
+   :maxdepth: 1
+   :caption: Guides
+
+   .. toctree::
+   :maxdepth: 1
+   :caption: Policies
+   cpu-specific-build-macros
+   exception-handling
+   firmware-design
+   firmware-update
+   interrupt-framework-design
+   platform-compatibility-policy
+   platform-interrupt-controller-API
+   porting-guide
+   psci-lib-integration-guide
+   psci-pd-tree
+   ras
+   reset-design
+   rt-svc-writers-guide
+   sdei
+   secure-partition-manager-design
+   trusted-board-boot
+   user-guide
+   xlat-tables-lib-v2-design
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`