drm/amd/display: Add work-around option to skip DCN20 clock updates

[Why] Auto Overclock Memory fails for some systems that don't support
p-state.

[How] Implement the workaround, and it's corresponding enable flag.

Signed-off-by: Jaehyun Chung <jaehyun.chung@amd.com>
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>