feat(rmmd): add FEAT_MEC support

This patch provides architectural support for further use of
Memory Encryption Contexts (MEC) by declaring the necessary
registers, bits, masks, helpers and values and modifying the
necessary registers to enable FEAT_MEC.

Signed-off-by: Tushar Khandelwal <tushar.khandelwal@arm.com>
Signed-off-by: Juan Pablo Conde <juanpablo.conde@arm.com>
Change-Id: I670dbfcef46e131dcbf3a0b927467ebf6f438fa4
diff --git a/lib/el3_runtime/aarch64/context_mgmt.c b/lib/el3_runtime/aarch64/context_mgmt.c
index e28e1c3..531edcb 100644
--- a/lib/el3_runtime/aarch64/context_mgmt.c
+++ b/lib/el3_runtime/aarch64/context_mgmt.c
@@ -548,6 +548,10 @@
 	}
 #endif /* (IMAGE_BL31 && defined(SPD_spmd) && SPMD_SPM_AT_SEL2) */
 
+	if (is_feat_mec_supported()) {
+		scr_el3 |= SCR_MECEn_BIT;
+	}
+
 	/*
 	 * Populate EL3 state so that we've the right context
 	 * before doing ERET