IOAPIC: Fix missing stdint include

Change-Id: Ib26f48d3ac66788246834cdc25d97910cd79fe98
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/6264
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

src/arch/x86/include/arch/ioapic.h

@@ -24,6 +24,9 @@
 #define IO_APIC_INTERRUPTS 24
 
 #ifndef __ACPI__
+
+#include <stdint.h>
+
 #define ALL		(0xff << 24)
 #define NONE		(0)
 #define DISABLED	(1 << 16)