drm/amdgpu: condense mqd programming sequence

The MQD structure matches the reg layout. Take advantage of this to
simplify HQD programming.

Note that the ACTIVE field still needs to be programmed last.

Suggested-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>