[why]
DSC target bpp precision is a decoder DPCD and an AMD encoder capability.
It must be taken into account when calculating target bitrate.

[how]
Add a DC DSC function that does this calculation.
Signed-off-by: NNikola Cornij <nikola.cornij@amd.com>
Reviewed-by: NWenjing Liu <Wenjing.Liu@amd.com>
Acked-by: NLeo Li <sunpeng.li@amd.com>
Acked-by: NHawking Zhang <Hawking.Zhang@amd.com>
Acked-by: NTony Cheng <Tony.Cheng@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>