Add unit tests for Pointer Authentication

Add unit tests to:
    Test access to the key registers.
    Use the pointer authentication instructions.
    Call psci version and check the EL3 pointer authentication keys
    aren't leaked.
    Make a tsp call and check the secure world keys aren't leaked.

Change-Id: Ic7940757e6f9fc905ccef8c035e0c22b47b35cd7
Signed-off-by: Joel Hutton <Joel.Hutton@Arm.com>
diff --git a/tftf/tests/tests-cpu-extensions.mk b/tftf/tests/tests-cpu-extensions.mk
index 38271dc..daf9528 100644
--- a/tftf/tests/tests-cpu-extensions.mk
+++ b/tftf/tests/tests-cpu-extensions.mk
@@ -10,4 +10,5 @@
 	extensions/sve/test_sve.c					\
 	runtime_services/arm_arch_svc/smccc_arch_workaround_1.c		\
 	runtime_services/arm_arch_svc/smccc_arch_workaround_2.c		\
+	extensions/ptrauth/test_ptrauth.c				\
 )