refactor(sgi): replace build-option prefix with "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", replace the prefix "CSS_SGI" with "NRD".

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I3ef01fedd6d955631bf39a3bf31c741cdeadf1cc
diff --git a/tf_config/fvp-rdn1edgex2-tbb b/tf_config/fvp-rdn1edgex2-tbb
index 85ebe1f..4d15046 100644
--- a/tf_config/fvp-rdn1edgex2-tbb
+++ b/tf_config/fvp-rdn1edgex2-tbb
@@ -2,7 +2,7 @@
 CREATE_KEYS=1
 CROSS_COMPILE=aarch64-none-elf-
 GENERATE_COT=1
-CSS_SGI_CHIP_COUNT=2
+NRD_CHIP_COUNT=2
 PLAT=rdn1edge
 ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem
 TRUSTED_BOARD_BOOT=1
diff --git a/tf_config/fvp-rdn2cfg3-tbb b/tf_config/fvp-rdn2cfg3-tbb
index 27c2809..67a5d74 100644
--- a/tf_config/fvp-rdn2cfg3-tbb
+++ b/tf_config/fvp-rdn2cfg3-tbb
@@ -1,7 +1,7 @@
 ARM_ROTPK_LOCATION=devel_rsa
 CREATE_KEYS=1
 CROSS_COMPILE=aarch64-none-elf-
-CSS_SGI_PLATFORM_VARIANT=3
+NRD_PLATFORM_VARIANT=3
 GENERATE_COT=1
 PLAT=rdn2
 ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem
diff --git a/tf_config/fvp-rdv1mc-tbb b/tf_config/fvp-rdv1mc-tbb
index c35a3fc..ddfcb0f 100644
--- a/tf_config/fvp-rdv1mc-tbb
+++ b/tf_config/fvp-rdv1mc-tbb
@@ -3,6 +3,6 @@
 CROSS_COMPILE=aarch64-none-elf-
 GENERATE_COT=1
 PLAT=rdv1mc
-CSS_SGI_CHIP_COUNT=4
+NRD_CHIP_COUNT=4
 ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem
 TRUSTED_BOARD_BOOT=1