drm/amd/display: DSC Bit target rate debugfs write entry

[Why]
We need to be able to specify bits per pixel for DSC on any
connector.

[How]
Overwrite computed DSC target rate in dsc_cfg, with requested value.
Overwrites for both SST and MST connectors, but in different places, but the process is identical. Overwrites only if DSC is decided to be enabled on that connector.

Signed-off-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Mikita Lipski <Mikita.Lipski@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>