fixing minor bugs with single unit compilation in gcc with flags on

kernel/io.h

@@ -1,6 +1,8 @@
 #ifndef IO_H
 #define IO_H
 
+#include <stdint.h>
+
 static inline void outb(uint16_t port, uint8_t val) {
     asm volatile ("outb %0, %1" : : "a"(val), "Nd"(port));
 }