src/include: Add missing includes

Change-Id: I746ea7805bae553a146130994d8174aa2e189610
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43368
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/include/cpu/cpu.h

@@ -2,6 +2,7 @@
 #define CPU_CPU_H
 
 #include <arch/cpu.h>
+#include <stdint.h>
 
 void cpu_initialize(unsigned int cpu_index);
 /* Returns default APIC id based on logical_cpu number or < 0 on failure. */