zynqmp: pm: Remove unnecessary header includes

Remove includes of gic_common.h and string.h which
are not required.

Signed-off-by: Rajan Vaja <rajanv@xilinx.com>
Acked-by: Jolly Shah <jollys@xilinx.com>

plat/xilinx/zynqmp/pm_service/pm_svc_main.c

@@ -10,9 +10,7 @@
  */
 
 #include <errno.h>
-#include <gic_common.h>
 #include <runtime_svc.h>
-#include <string.h>
 #include "../zynqmp_private.h"
 #include "pm_api_sys.h"
 #include "pm_client.h"