Revert "drm/amd/display: enable DPG when disabling plane for phantom pipe"

This reverts commit d47d2f93.

regression detected by the change. Revert until
fix is available.

Signed-off-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>