Fix coding guideline warnings

This patch fixes some coding guideline warnings reported by the checkpatch
script. Only files related to upcoming feature development have been fixed.

Change-Id: I26fbce75c02ed62f00493ed6c106fe7c863ddbc5
diff --git a/services/std_svc/psci/psci_common.c b/services/std_svc/psci/psci_common.c
index a651d99..2a0afb4 100644
--- a/services/std_svc/psci/psci_common.c
+++ b/services/std_svc/psci/psci_common.c
@@ -817,7 +817,7 @@
 	plat_local_state_type_t state_type;
 
 	/* This array maps to the PSCI_STATE_X definitions in psci.h */
-	static const char *psci_state_type_str[] = {
+	static const char * const psci_state_type_str[] = {
 		"ON",
 		"RETENTION",
 		"OFF",