plat/sgi: improve macros defining cper buffer memory region

Remove the 'ARM_' prefix from the macros defining the CPER buffer memory
and replace it with 'CSS_SGI_' prefix. These macros are applicable only
for platforms supported within plat/sgi. In addition to this, ensure
that these macros are defined only if the RAS_EXTENSION build option is
enabled.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I44df42cded18d9d3a4cb13e5c990e9ab3194daee
2 files changed