drm/amd/powerplay: slow UCLK switch when multiple displays not in sync

Slow switch for UCLK when there is multiple displays and they are
not in sync.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Rex Zhu <rex.zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>