drm/display/dsc: add helper to set semi-const parameters

drm/display/dsc: add helper to set semi-const parameters

Add a helper setting config values which are typically constant across
operating modes (table E-4 of the standard) and mux_word_size (which is
a const according to 3.5.2).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/539280/
Link: https://lore.kernel.org/r/20230329-rfc-msm-dsc-helper-v14-2-bafc7be95691@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>