build: add build configs for infra-rd platforms in tftf

Add tftf build configs for the following infra-rd platforms:
* rdv1
* rdn2
* rdn2cfg1

Signed-off-by: Shriram K <shriram.k@arm.com>
Change-Id: I8d61a225fba20c5c3d9c914c22bf599ada100bd4
diff --git a/tftf_config/fvp-rdn2-default b/tftf_config/fvp-rdn2-default
new file mode 100644
index 0000000..aea2b19
--- /dev/null
+++ b/tftf_config/fvp-rdn2-default
@@ -0,0 +1,3 @@
+CROSS_COMPILE=aarch64-none-elf-
+CSS_SGI_PLATFORM_VARIANT=0
+PLAT=rdn2