feat: support Cactus SP to boot on EL3 SPMC

EL3 SPMC has a limited set of FF-A functionality and does not support
all the features built into the current Cactus SP implementation.

Hence, this patch introduces a build option to strip out few features
from Cactus SP in order to boot it on EL3 SPMC.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I6319563adca67460015b79219ebc5c9468e3d54a
diff --git a/spm/cactus/cactus_main.c b/spm/cactus/cactus_main.c
index 28afbfb..b608d7b 100644
--- a/spm/cactus/cactus_main.c
+++ b/spm/cactus/cactus_main.c
@@ -324,12 +324,14 @@
 		EXPECT(ffa_func_id(ret), FFA_SUCCESS_SMC32);
 	}
 
+#if !SPMC_AT_EL3
 	discover_managed_exit_interrupt_id();
 	register_maintenance_interrupt_handlers();
 
 	/* Invoking self tests */
 	ffa_tests(&mb, true);
 	cpu_feature_tests();
+#endif
 
 msg_loop:
 	/* End up to message loop */