[util] Move enum_bitfields into util

Continuing on the cleaning up of the src/include 'junk drawer', the
enum_bitfields.h and its dependency basic_types.h are now in util.

src/kernel/page_table.h

@@ -4,8 +4,8 @@
 
 #include <stdint.h>
 #include <arch/memory.h>
+#include <util/enum_bitfields.h>
 #include <util/spinlock.h>
-#include <enum_bitfields.h>
 
 struct free_page_header;