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/sd_card.h

@@ -0,0 +1,18 @@
+#ifndef _SD_CARD_H
+#define _SD_CARD_H
+
+#include <stdint.h>
+
+void sd_init();
+uint16_t sd_get_rca();
+uint16_t sd_select_card(uint16_t rca);
+uint16_t sd_get_status(uint16_t rca);
+void sd_readblock(uint32_t addr, void* buf);
+
+void sd_card_command(uint32_t arg, uint8_t cmd);
+
+void sd_card_resp(uint32_t* resp);
+uint8_t sd_card_read_byte();
+void sd_card_wait_for_data();
+
+#endif