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>
diff --git a/docs/user-guide.rst b/docs/user-guide.rst
index 4df7590..d175ebd 100644
--- a/docs/user-guide.rst
+++ b/docs/user-guide.rst
@@ -219,7 +219,8 @@
 
 -  ``ARM_ARCH_MAJOR``: The major version of ARM Architecture to target when
    compiling ARM Trusted Firmware. Its value must be numeric, and defaults to
-   8 . See also, *ARMv8 Architecture Extensions* in `Firmware Design`_.
+   8 . See also, *ARMv8 Architecture Extensions* and
+   *ARMv7 Architecture Extensions* in `Firmware Design`_.
 
 -  ``ARM_ARCH_MINOR``: The minor version of ARM Architecture to target when
    compiling ARM Trusted Firmware. Its value must be a numeric, and defaults