refactor(sgi): replace build-option prefix to "NRD"

As of now, CSS_SGI_PLATFORM_VARIANT and CSS_SGI_CHIP_COUNT are the
external build option that "sgi" platforms support. As "sgi" has been
renamed to "neoverse_rd" and the source files have been migrated out of
the css directory, replace the prefix "CSS_SGI" with "NRD".

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I27989ff42404d823dd2a8cd22ff485497ccb62d4
diff --git a/plat/arm/board/neoverse_rd/common/nrd-common.mk b/plat/arm/board/neoverse_rd/common/nrd-common.mk
index 33da19c..96e6f01 100644
--- a/plat/arm/board/neoverse_rd/common/nrd-common.mk
+++ b/plat/arm/board/neoverse_rd/common/nrd-common.mk
@@ -16,9 +16,9 @@
 
 HANDLE_EA_EL3_FIRST_NS		:=	0
 
-CSS_SGI_CHIP_COUNT		:=	1
+NRD_CHIP_COUNT		:=	1
 
-CSS_SGI_PLATFORM_VARIANT	:=	0
+NRD_PLATFORM_VARIANT	:=	0
 
 # Do not enable SVE
 ENABLE_SVE_FOR_NS		:=	0
@@ -58,9 +58,9 @@
   Please set RESET_TO_BL31 to 0.")
 endif
 
-$(eval $(call add_define,CSS_SGI_CHIP_COUNT))
+$(eval $(call add_define,NRD_CHIP_COUNT))
 
-$(eval $(call add_define,CSS_SGI_PLATFORM_VARIANT))
+$(eval $(call add_define,NRD_PLATFORM_VARIANT))
 
 override CSS_LOAD_SCP_IMAGES	:=	0
 override NEED_BL2U		:=	no