[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/libraries/elf/include/elf/headers.h

@@ -1,6 +1,6 @@
 #pragma once
 #include <stdint.h>
-#include "enum_bitfields.h"
+#include <util/enum_bitfields.h>
 
 namespace elf {
 
@@ -61,6 +61,7 @@ enum class segment_flags : uint32_t
     write = 0x02,
     read  = 0x04,
 };
+is_bitfield(segment_flags);
 
 struct program_header
 {