drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits

drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits

drm_dsc_config's bits_per_pixel field holds a fractional value with 4
bits, which all panel drivers should adhere to for
drm_dsc_pps_payload_pack() to generate a valid payload.  All code in the
DSI driver here seems to assume that this field doesn't contain any
fractional bits, hence resulting in the wrong values being computed.
Since none of the calculations leave any room for fractional bits or
seem to indicate any possible area of support, disallow such values
altogether.  calculate_rc_params() in intel_vdsc.c performs an identical
bitshift to get at this integer value.

Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/508938/
Link: https://lore.kernel.org/r/20221026182824.876933-8-marijn.suijten@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>