n1sdp: Add support for n1sdp in ci

Build scp and tf-a and test the artefacts on n1sdp in LAVA.

Change-Id: Iabe1bc65c5eb18f3204ec732fa259e7e6a4351bc
Signed-off-by: Khasim Syed Mohammed <khasim.mohammed@arm.com>
diff --git a/tf_config/n1sdp-default b/tf_config/n1sdp-default
index 4125932..aa2ef2b 100644
--- a/tf_config/n1sdp-default
+++ b/tf_config/n1sdp-default
@@ -1,2 +1,3 @@
 CROSS_COMPILE=aarch64-none-elf-
 PLAT=n1sdp
+SCP_BL2=/dev/null