Refactor GIC header files

Move the function prototypes from gic.h into either gic_v2.h or
gic_v3.h as appropriate. Update the source files to include the
correct headers.

Change-Id: I368cfda175cdcbd3a68f46e2332738ec49048e19
diff --git a/plat/fvp/plat_pm.c b/plat/fvp/plat_pm.c
index 2a414c9..4359638 100644
--- a/plat/fvp/plat_pm.c
+++ b/plat/fvp/plat_pm.c
@@ -38,7 +38,7 @@
 #include <bl31.h>
 #include <bakery_lock.h>
 #include <cci400.h>
-#include <gic.h>
+#include <gic_v2.h>
 /* Only included for error codes */
 #include <psci.h>
 #include "drivers/pwrc/fvp_pwrc.h"