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/tftf_config/fvp-rdn2-default b/tftf_config/fvp-rdn2-default
index aea2b19..3ff912a 100644
--- a/tftf_config/fvp-rdn2-default
+++ b/tftf_config/fvp-rdn2-default
@@ -1,3 +1,3 @@
 CROSS_COMPILE=aarch64-none-elf-
-CSS_SGI_PLATFORM_VARIANT=0
+NRD_PLATFORM_VARIANT=0
 PLAT=rdn2
diff --git a/tftf_config/fvp-rdn2cfg1-default b/tftf_config/fvp-rdn2cfg1-default
index 4be48dc..dc5e4fb 100644
--- a/tftf_config/fvp-rdn2cfg1-default
+++ b/tftf_config/fvp-rdn2cfg1-default
@@ -1,3 +1,3 @@
 CROSS_COMPILE=aarch64-none-elf-
-CSS_SGI_PLATFORM_VARIANT=1
+NRD_PLATFORM_VARIANT=1
 PLAT=rdn2
diff --git a/tftf_config/fvp-rdn2cfg3-default b/tftf_config/fvp-rdn2cfg3-default
index f5bbda1..ae2117c 100644
--- a/tftf_config/fvp-rdn2cfg3-default
+++ b/tftf_config/fvp-rdn2cfg3-default
@@ -1,3 +1,3 @@
 CROSS_COMPILE=aarch64-none-elf-
-CSS_SGI_PLATFORM_VARIANT=3
+NRD_PLATFORM_VARIANT=3
 PLAT=rdn2