drm/amd/display: Handle SMU msg response

[Why]
SMU may return error code to driver, but driver only check if response
is OK.

[How]
Check SMU response instead of reg_wait, assert in case of reponse isn't
OK.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>