Separate kernel code from test code

Eventually I want the kernel to be loaded from the SD card as well, but
it still needs to separate from user programs.

At some point there should be a folder just for the BIOS, which should
read from the boot block of the SD card and start executing, and thats
it.

sw/kernel/devices/board_io.h

@@ -0,0 +1,16 @@
+#ifndef _BOARD_IO_H
+#define _BOARD_IO_H
+
+#include <stdint.h>
+
+uint8_t hex_set_8(uint8_t val, uint8_t idx);
+uint8_t hex_set_16(uint16_t val);
+uint8_t hex_set_24(uint32_t val);
+
+void hex_enable(uint8_t mask);
+
+uint8_t sw_read();
+
+void led_set(uint8_t val);
+
+#endif