drivers/gic/gic: add missing arch/cpu.h include

smp_processor_id is defined in src/arch/arm64/include/armv8/arch/cpu.h.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I0b610189bf439774cb900f74559dee314cbc5854
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57728
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/drivers/gic/gic.c

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <arch/cpu.h>
 #include <device/mmio.h>
 #include <console/console.h>
 #include <gic.h>