Add driver for hex digits

This only includes the method to set the pairs of displays individually.
The functions to write a single 16 or 32 bit value have not been
implemented yet, nor has the mask function.

sw/main.c

@@ -1,11 +1,12 @@
-#define SEVEN_SEG 0x7ff0
-
 #include <stdint.h>
 
-int main() {
-    uint16_t* seven_seg;
-    seven_seg = (uint16_t*)SEVEN_SEG;
+#include "sevenseg.h"
 
-    *seven_seg = 0xbabe;
+int main() {
+    //hex_enable(0xff);
+    hex_set_8(0xb5, 0);
+    hex_set_8(0x00, 1);
+    hex_set_8(0xb0, 2);
+    while(1);
     return 0;
 }