drm/amdgpu/psp: initial vega12 support

Same as vega10 for now.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>