drm/msm/dsi: Replace dsi_get_bpp() with mipi_dsi header function

drm_mipi_dsi.h already provides a conversion function from MIPI_DSI_FMT_
to bpp, named mipi_dsi_pixel_format_to_bpp().

Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/577065/
Link: https://lore.kernel.org/r/20240204-drm-msm-dsi-remove-open-coded-get-bpp-v1-1-c16212de7e86@somainline.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>