ARMv7 target is driven by ARM_ARCH_MAJOR==7 ...

External build environment shall sets directive ARM_ARCH_MAJOR to 7
to specify a target ARMv7-A core.

As ARM-TF expects AARCH to be set, ARM_ARCH_MAJOR==7 mandates
AARCH=aarch32.

The toolchain target architecture/cpu is delegated after the platform
configuration is parsed. Platform shall define target core through
ARM_CORTEX_A<x>=yes, <x> being 5, 7, 9, 12, 15 and/or 17.

Platform can bypass ARM_CORTEX_A<x>=yes directive and provide straight
the toolchain target directive through MARCH32_DIRECTIVE.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>

Convert documentation to reStructuredText ...

Due to recent issues in the rendering of the documentation on GitHub and
some long-standing issues like the lack of automatic table of content in
Markdown, the documentation has been converted to reStructuredText.
Basic constructs looks pretty similar to Markdown.

Automatically convert GitHub markdown documentation to reStructuredText
using pandoc.

Change-Id: If20b695acedc6d1b49c8d9fb64efd6b6ba23f4a9
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>