doc: Add and correct headings for imported files

Some files imported from the wiki are missing RST section headers and
other files are using inconsistent characters for the same header level.

Change-Id: I318c843f9bc8fb40074ef90827b9acac06463662
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

docs/frequently-asked-questions.rst

+Frequently-Asked Questions (FAQ)
+================================
+
 How do I update a Pull Request?
 -------------------------------
 

docs/image-terminology.rst

-Trusted Firmware images
------------------------
+Image Terminology
+=================
+
+.. section-numbering::
+    :suffix: .
+
+.. contents::
 
 This page contains the current name, abbreviated name and purpose of the various
 images referred to in the Trusted Firmware project.
 
-Some general notes:
+General Notes
+-------------
 
 - Some of the names and abbreviated names have changed to accomodate new
   requirements. The changed names are as backward compatible as possible to
@@ -36,6 +42,9 @@ Some general notes:
 - The image names are not case sensitive. For example, ``bl1`` is
   interchangeable with ``BL1``, although mixed case should be avoided.
 
+Trusted Firmware Images
+-----------------------
+
 AP Boot ROM: ``AP_BL1``
 ~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -114,8 +123,8 @@ This image was previously abbreviated as BL3-0 but from the SCP's point of view,
 this has always been the 2nd stage firmware. The previous name is too
 AP-centric.
 
-Firmware update images
-----------------------
+Firmware Update (FWU) Images
+----------------------------
 
 The terminology for these images has not been widely adopted yet but they have
 to be considered in a production Trusted Board Boot solution.
@@ -154,7 +163,7 @@ This is the 2nd stage AP normal world firmware updater. Its primary purpose is
 to load a new set of firmware images from an external interface and write them
 into non-volatile storage.
 
-Other processor firmware images
+Other Processor Firmware Images
 -------------------------------
 
 Some systems may have additional processors to the AP and SCP. For example, a

docs/psci-performance-juno.rst

+PSCI Performance Measurements on Arm Juno Development Platform
+==============================================================
+
 This document summarises the findings of performance measurements of key
 operations in the ARM Trusted Firmware (TF) Power State Coordination Interface
 (PSCI) implementation, using the in-built Performance Measurement Framework

docs/security-center.rst

+Security Center
+===============
+
 Security Disclosures
 --------------------