[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/apic.h

@@ -3,7 +3,7 @@
 /// Classes to control both local and I/O APICs.
 
 #include <stdint.h>
-#include "enum_bitfields.h"
+#include <util/enum_bitfields.h>
 
 enum class isr : uint8_t;