arm-bsp/tf-a-tests: Add recipe to build and install TFTF

TFTF is TF-A tests that runs at NS-EL2. This is primarily developed to
test the TF-A interfaces exposed to NS code.

Signed-off-by: Vishnu Banavath <vishnu.banavath@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

kas/tftf.yml

@@ -0,0 +1,7 @@
+header:
+  version: 9
+
+local_conf_header:
+  tftf: |
+    TFA_UBOOT = "0"
+    TFTF_TESTS = "1"