drm/amd/display: Add changes for dsc bpp in 16ths and unify bw calculations

[Why?]
Some code still expected bpp to be used in whole bits, not 16ths.  dsc.c uses
redundant function now found in dc to calculate stream bandwidth from timing.

[How?]
Fix code to work with 16ths instead of whole bits for dsc bpp.
Refactor get_dsc_bandwidth to accept inputs in 16ths of a bit.
Use dc function to calculate bandwidth from timing, and make dsc bw calculation
a part of dsc.c.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>