feat(spmc): add FFA_FEATURES handler

Enable the spmc to report the features that it currently supports.
Populated with the currently implemented functionality.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: I00e51ded284efd87cd50a0e9416dbc33f22ced85
diff --git a/services/std_svc/spm/el3_spmc/spmc.h b/services/std_svc/spm/el3_spmc/spmc.h
index 1afd688..d383a65 100644
--- a/services/std_svc/spm/el3_spmc/spmc.h
+++ b/services/std_svc/spm/el3_spmc/spmc.h
@@ -37,6 +37,9 @@
 #define FFA_WB_TYPE_S2RAM	0
 #define FFA_WB_TYPE_NOTS2RAM	1
 
+/* FF-A Related helper macros. */
+#define FFA_FEATURES_BIT31_MASK		U(0x1u << 31)
+
 #define FFA_PAGE_SIZE (4096)
 #define FFA_RXTX_PAGE_COUNT_MASK 0x1F