build: add build config for rdn2cfg3 in tf and tftf

Add tf and tftf build configs for infra-rd platform rdn2cfg3

Signed-off-by: Tony K Nadackal <tony.nadackal@arm.com>
Change-Id: I483886898920ebd74d5003661528479b0ae2c2fc
diff --git a/tftf_config/fvp-rdn2cfg3-default b/tftf_config/fvp-rdn2cfg3-default
new file mode 100644
index 0000000..f5bbda1
--- /dev/null
+++ b/tftf_config/fvp-rdn2cfg3-default
@@ -0,0 +1,3 @@
+CROSS_COMPILE=aarch64-none-elf-
+CSS_SGI_PLATFORM_VARIANT=3
+PLAT=rdn2