feat(gic600ae_fmu): introduce support for RAS error handling

The GIC-600AE uses a range of RAS features for all RAMs, which include
SECDED, ECC, and Scrub, software and bus error reporting. The GIC makes
all necessary information available to software through Armv8.2 RAS
architecture compliant register space.

This patch introduces support to probe the FMU_ERRGSR register to find
the right error record. Once the correct record is identified, the
"handler" function queries the FMU_ERR<m>STATUS register to further
identify the block ID, safety mechanism and the architecturally defined
primary error code. The description of the error is displayed on the
console to simplify debug.

Change-Id: I7e543664b74457afee2da250549f4c3d9beb1a03
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>