Newer asics need 64 bit doorbells.

v2: fix comment (Nils)
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NKen Wang <Qingqing.Wang@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>