Making the capabilities register a union makes it easier to refer
to the members instead of always doing bit shifts.

No intended functional changes.
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Suggested-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>