Add support for documentation build as a target in Makefile ...

Command to build HTML-formatted pages from docs:
make doc

Change-Id: I4103c804b3564fe67d8fc5a3373679daabf3f2e9
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

docs: Creating a Change Log Template File ...

Creating a Change Log Template for ALL to update with relevant
new features, changes, fixes and known issues for each upcoming
release of Trusted Firmware-A.

The contents of this file should be added to the collective change log
at the time of release code freeze.

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Change-Id: Idfbdcef0d40b10312dc88b6e1cbe31856fda887e