mmu: Add initial implementation of identity mapping

kernel/start_kernel.c

@@ -1,3 +1,4 @@
+#include <mmu.h>
 #include <mm.h>
 #include <print.h>
 #include <devices/pl011.h>
@@ -54,6 +55,10 @@ void test_memory() {
  
 int main(void) {
 	char *lower;
+
+	//setup MMU
+	mmu_reinit();
+
 	print_init(&pl011_putc); //initialize the serial console
 
 	//setup memory