arm64: Remove cpu intialization through device-tree

Since, SMP support is removed for ARM64, there is no need for CPU
initialization to be performed via device-tree.

Change-Id: I0534e6a93c7dc8659859eac926d17432d10243aa
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: http://review.coreboot.org/11913
Tested-by: build bot (Jenkins)
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/drivers/gic/gic.c

@@ -17,6 +17,7 @@
 #include <arch/io.h>
 #include <console/console.h>
 #include <gic.h>
+#include <stddef.h>
 #include "gic.h"
 
 enum {