cactus: implement hvc call to get interrupt id

Since an SP cannot access GIC directly, it relies on SPMC(S-EL2) to
get the interrupt ID.
This patch introduces a new hvc call "SPM_INTERRUPT_GET" to get
interrupt ID in S-EL1.

Change-Id: I37626f907174ae57a24dc6b86e89d26ba8ebbddf
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
diff --git a/spm/common/sp_helpers.c b/spm/common/sp_helpers.c
index 2345051..1b650d3 100644
--- a/spm/common/sp_helpers.c
+++ b/spm/common/sp_helpers.c
@@ -75,6 +75,17 @@
  * Hypervisor Calls Wrappers
  ******************************************************************************/
 
+ffa_int_id_t spm_interrupt_get(void)
+{
+	hvc_args args = {
+		.fid = SPM_INTERRUPT_GET
+	};
+
+	hvc_ret_values ret = tftf_hvc(&args);
+
+	return ret.ret0;
+}
+
 void spm_debug_log(char c)
 {
 	hvc_args args = {