refactor(cpufeat): align FEAT_SEL2 to new feature handling

In ARMv8.4, the EL2 exception level got added to the secure world.
Adapt and rename the existing is_armv8_4_sel2_present() function, to
align its handling with the other CPU features.

Change-Id: If11e1942fdeb63c63f36ab9e89be810347d1a952
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/services/std_svc/spmd/spmd_main.c b/services/std_svc/spmd/spmd_main.c
index e85109d..0e1899e 100644
--- a/services/std_svc/spmd/spmd_main.c
+++ b/services/std_svc/spmd/spmd_main.c
@@ -399,7 +399,7 @@
 	 * Check if S-EL2 is supported on this system if S-EL2
 	 * is required for SPM
 	 */
-	if (!is_armv8_4_sel2_present()) {
+	if (!is_feat_sel2_supported()) {
 		WARN("SPM Core run time S-EL2 is not supported.\n");
 		return -EINVAL;
 	}