drm/amd/display: split dccg clock manager into asic folders

Currently dccg contains code related to every dcn revision in
a single file.

This change splits out the dcn parts of code into correct folders

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>