nb/intel/x4x.h: Include stdint.h

The structs and function definition in that header require it.

Change-Id: I3466ff1a28459d0285e27d368314faf747e2eac1
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36769
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/northbridge/intel/x4x/x4x.h

@@ -18,6 +18,7 @@
 #ifndef __NORTHBRIDGE_INTEL_X4X_H__
 #define __NORTHBRIDGE_INTEL_X4X_H__
 
+#include <stdint.h>
 #include "iomap.h"
 
 /*