test(interrupts): exercise ns interrupt being signaled to SP

This patch adds a tftf based test to exercise non-secure interrupt
handling being signaled to the Cactus SP by the SPMC while processing
a direct message.

A detailed description is provided in the comment leading the test
function.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I2f8511135470d2ca8f567532a1cb7c4ae374af3f
diff --git a/include/runtime_services/cactus_test_cmds.h b/include/runtime_services/cactus_test_cmds.h
index 1e60e0e..d86aa61 100644
--- a/include/runtime_services/cactus_test_cmds.h
+++ b/include/runtime_services/cactus_test_cmds.h
@@ -24,6 +24,10 @@
 #define CACTUS_ERROR_FFA_CALL		U(3)
 #define CACTUS_ERROR_UNHANDLED		U(4)
 
+#define ECHO_VAL1 U(0xa0a0a0a0)
+#define ECHO_VAL2 U(0xb0b0b0b0)
+#define ECHO_VAL3 U(0xc0c0c0c0)
+
 /**
  * Get command from struct ffa_value.
  */