arch/x86/boot: Add missing include

This file uses the asmlinkage macro.

BUG=b:179699789
TEST=build guybrush

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Change-Id: Id5b73c174aa946b8205b4172609729b0548cbd8c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57567
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/arch/x86/boot.c

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <arch/boot/boot.h>
+#include <arch/cpu.h>
 #include <commonlib/helpers.h>
 #include <console/console.h>
 #include <program_loading.h>