libblkid: convert GPT attributes to host endianess

Signed-off-by: Karel Zak <kzak@redhat.com>
libfdisk: (gpt) use entry attributes as bitmap

 * care about endianess
 * don't use by compiler packed struct with bit array for GPT
   attributes, it's more robust use it as bitmap stored in uint64_t.

Signed-off-by: Karel Zak <kzak@redhat.com>