drm/amd/display: Implement DTBCLK ref switching on dcn32

[WHY & HOW]
Implements DTB ref clock switching with reg key default to OFF.
Refactors dccg DTBCLK logic to not store redundant state information
dccg. Also removes duplicated functions that should be inherited from
other dcn versions.

Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>