drm/amd/display: Cleanup DML DSC input bpc validation

[Why & How]
Pipe input DSC bpc has a type mismatch with maximum DSC
input bpc - align the maximum with the pipe input type,
unsigned integer.

When checking the type we shoudl also check for an
implicit value of 0 and align with what the spreadsheet
does - default to max.

Rename output_bpc to dsc_input_bpc to reflect what the
field is actually used for.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>