fix(ras): remove RAS_FFH_SUPPORT and introduce FFH_SUPPORT

This patch removes RAS_FFH_SUPPORT macro which is the combination of
ENABLE_FEAT_RAS and HANDLE_EA_EL3_FIRST_NS. Instead introduce an
internal macro FFH_SUPPORT which gets enabled when platforms wants
to enable lower EL EA handling at EL3. The internal macro FFH_SUPPORT
will be automatically enabled if HANDLE_EA_EL3_FIRST_NS is enabled.
FFH_SUPPORT along with ENABLE_FEAT_RAS will be used in source files
to provide equivalent check which was provided by RAS_FFH_SUPPORT
earlier. In generic code we needed a macro which could abstract both
HANDLE_EA_EL3_FIRST_NS and RAS_FFH_SUPPORT macros that had limitations.
Former was tied up with NS world only while the latter was tied to RAS
feature.

This is to allow Secure/Realm world to have their own FFH macros
in future.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: Ie5692ccbf462f5dcc3f005a5beea5aa35124ac73
diff --git a/docs/getting_started/build-internals.rst b/docs/getting_started/build-internals.rst
index a015d71..390c367 100644
--- a/docs/getting_started/build-internals.rst
+++ b/docs/getting_started/build-internals.rst
@@ -12,3 +12,10 @@
    interest when Armv8.4-SecEL2 or RME extension is implemented.
    Default is 0 (disabled). This option will be set to 1 (enabled) when ``SPD=spmd``
    and ``SPMD_SPM_AT_SEL2`` is set or when ``ENABLE_RME`` is set to 1 (enabled).
+
+- ``FFH_SUPPORT``: This boolean option provides support to enable Firmware First
+  handling (FFH) of External aborts and SError interrupts originating from lower
+  ELs which gets trapped in EL3. This option will be set to 1 (enabled) if
+  ``HANDLE_EA_EL3_FIRST_NS`` is set. Currently only NS world routes EA to EL3 but
+  in future when Secure/Realm wants to use FFH then they can introduce new macros
+  which will enable this option implicitly.