mm: fix page frame allocator bugs

This also includes a minor refactor of everything,
as well as some optimizations.  The bitmap
operations have been moved into a separate file
because they are probably gonna come in handy in
other parts of the system as well.

kernel/mm/kmalloc.c

@@ -3,6 +3,7 @@
 #include <gay/kprintf.h>
 #include <gay/mm.h>
 #include <gay/types.h>
+#include <gay/util.h>
 
 extern void _image_start_phys;
 extern void _image_end_phys;