feat(intel): add build config and variant for N5X

Add build config and variant for Intel N5X platforms.

Signed-off-by: Sieu Mun Tang <sieu.mun.tang@intel.com>
Change-Id: I44c7d8f50244e79bb3f5773157fbef0f892a2c85
diff --git a/tf_config/n5x-default b/tf_config/n5x-default
new file mode 100644
index 0000000..5086d4f
--- /dev/null
+++ b/tf_config/n5x-default
@@ -0,0 +1,2 @@
+CROSS_COMPILE=aarch64-none-elf-
+PLAT=n5x