src: Add missing include <stdint.h>

Change-Id: I6a9d71e69ed9230b92f0f330875515a5df29fc06
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/29312
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/riscv/include/arch/pmp.h

@@ -16,6 +16,8 @@
 #ifndef __RISCV_PMP_H__
 #define __RISCV_PMP_H__
 
+#include <stdint.h>
+
 /*
  * this function needs to be implemented by a specific SoC.
  * return number of PMP entries for current hart