drm/amd/display: Move call to disable DPG

[WHY]
Disabling DPG should happen after setting watermarks and clocks

Signed-off-by: Wesley Chalmers <wchalmer@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>