Add serial driver and irq support

sw/kernel/devices/serial.h

@@ -0,0 +1,17 @@
+#ifndef _SERIAL_H
+#define _SERIAL_H
+
+#include <stdint.h>
+
+void serial_handle_irq();
+
+void serial_init();
+
+void serial_putc(char c);
+void serial_puts(char* s);
+
+
+char serial_getc();
+char serial_getc_nb();
+
+#endif