Rename boot to bios, add sd call

Adds a call that you can make to the BIOS to read sd blocks. Useful for
the bootloader where there is not much space

sw/bios/load_bootsect.c

@@ -0,0 +1,29 @@
+#include <stdint.h>
+
+#include "devices/sd_card.h"
+
+#define BOOTSECTOR_LOAD_ADDRESS 0x1000
+
+#define BOOTSIG_0 0x55
+#define BOOTSIG_1 0xaa
+
+//Should probably do this in asm
+void load_bootsect() {
+    uint32_t rca;
+    uint8_t sig[2];
+    
+    sd_init();
+	rca = sd_get_rca();
+	sd_select_card(rca);
+
+    sd_readblock(0, (uint8_t*)BOOTSECTOR_LOAD_ADDRESS);
+
+    sig[0] = ((uint8_t*)BOOTSECTOR_LOAD_ADDRESS)[510];
+    sig[1] = ((uint8_t*)BOOTSECTOR_LOAD_ADDRESS)[511];
+
+    if (sig[0] != BOOTSIG_0 || sig[1] != BOOTSIG_1) {
+        for(;;);    //maybe figure out a way to have an error message here
+    }
+
+    return;
+}