feat(rmmd): verify FEAT_MEC present before calling plat hoook

Some platforms do not support FEAT_MEC. Hence, they do not provide
an interface to update the update of the key corresponding to a
MECID.

This patch adds a condition in order to verify FEAT_MEC is present
before calling the corresponding platform hook, thus preventing it
from being called when the platform does not support the feature.

Change-Id: Ib1eb9e42f475e27ec31529569e888b93b207148c
Signed-off-by: Juan Pablo Conde <juanpablo.conde@arm.com>
diff --git a/services/std_svc/rmmd/rmmd_main.c b/services/std_svc/rmmd/rmmd_main.c
index e94b048..9f9894e 100644
--- a/services/std_svc/rmmd/rmmd_main.c
+++ b/services/std_svc/rmmd/rmmd_main.c
@@ -479,6 +479,14 @@
 	int ret;
 
 	/*
+	 * Check whether FEAT_MEC is supported by the hardware. If not, return
+	 * unknown SMC.
+	 */
+	if (is_feat_mec_supported() == false) {
+		return E_RMM_UNK;
+	}
+
+	/*
 	 * Check whether the mecid parameter is at most MECIDR_EL2.MECIDWidthm1 + 1
 	 * in length.
 	 */