Include stdint.h in libpayload's rdtsc.h.

This file uses uint*_t types but hadn't included stdint.h itself.

Change-Id: Ib883f62951bae1ece5134c6bd0f4799a80740e8e
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/1720
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
Tested-by: build bot (Jenkins)

payloads/libpayload/include/i386/arch/rdtsc.h

@@ -30,6 +30,8 @@
 #ifndef _ARCH_RDTSC_H
 #define _ARCH_RDTSC_H
 
+#include <stdint.h>
+
 static u64 rdtsc(void)
 {
 	u64 val;