Write a significant chunk of coldboot init...

...merge start.cold.s and start.warm.s, other changes, etc.

exosphere/warmboot_main.c

@@ -0,0 +1,11 @@
+#include "utils.h"
+#include "mmu.h"
+#include "memory_map.h"
+
+extern void __jump_to_lower_el(uint64_t arg, uintptr_t ep, unsigned int el);
+
+void warmboot_main(void);
+
+void warmboot_main(void) {
+    /* TODO */
+}