drm/amd/display: Do not commit pipe when updating DRR

[WHY]
DRR and Pipe cannot be updated on
the same frame, or else underflow will
occur.

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