drm/amd/display: add a option to force the clock at every mode change.

[Description]
This is for HW negative stress testing use.
force reset the dispclk and dppclk even the same clock already set in HW.

Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>