Add: nonworking serial port driver implementation

kmain.c

@@ -1,8 +1,10 @@
 #include "stdio.h"
+#include "serial.h"
 
 int kmain(int retvalue)
 {
   clear();
   puts("hello\nbrave\nnew\nworld");
+  serial_write("hello", 1);
   return retvalue;
 }