arch/io.h: Add missing includes

Fixes indirect includes that would break with followup work.

Change-Id: I37ca01b904a0b422a4d09475377e755e167a6ab3
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/31697
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/soc/intel/quark/reg_access.c

@@ -15,6 +15,7 @@
 
 #define __SIMPLE_DEVICE__
 
+#include <arch/io.h>
 #include <assert.h>
 #include <cpu/x86/mtrr.h>
 #include <console/console.h>