Fix up doorbell setup and clockgating.

v2: squash in fixes (Alex)
Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Signed-off-by: Veerabadhran Gopalakrishnan <veerabadhran.gopalakrishnan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>