feat(interrupts): discover interrupt ID of managed exit signal

Added support for discovering managed exit interrupt ID in Cactus SP
using FFA_FEATURES ABI during partition initialization.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I0b6ea04fc18d6903d821e2f890e4e0a4ad5d568a
diff --git a/spm/cactus/cactus_main.c b/spm/cactus/cactus_main.c
index 5a274f6..8cd4cf1 100644
--- a/spm/cactus/cactus_main.c
+++ b/spm/cactus/cactus_main.c
@@ -316,6 +316,7 @@
 	cactus_print_memory_layout(ffa_id);
 
 	register_secondary_entrypoint();
+	discover_managed_exit_interrupt_id();
 
 	/* Invoking Tests */
 	ffa_tests(&mb);