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
diff --git a/plat/arm/css/sgi/sgi_plat.c b/plat/arm/css/sgi/sgi_plat.c
index 39eb89e..118bd22 100644
--- a/plat/arm/css/sgi/sgi_plat.c
+++ b/plat/arm/css/sgi/sgi_plat.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2021, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -81,7 +81,9 @@
 	PLAT_ARM_SECURE_MAP_DEVICE,
 	ARM_SP_IMAGE_MMAP,
 	ARM_SP_IMAGE_NS_BUF_MMAP,
-	ARM_SP_CPER_BUF_MMAP,
+#if RAS_EXTENSION
+	CSS_SGI_SP_CPER_BUF_MMAP,
+#endif
 	ARM_SP_IMAGE_RW_MMAP,
 	ARM_SPM_BUF_EL0_MMAP,
 	{0}