drm/display: split DSC helpers from DP helpers

drm/display: split DSC helpers from DP helpers

Currently the DRM DSC functions are selected by the
DRM_DISPLAY_DP_HELPER Kconfig symbol. This is not optimal, since the DSI
code (both panel and host drivers) end up selecting the seemingly
irrelevant DP helpers. Split the DSC code to be guarded by the separate
DRM_DISPLAY_DSC_HELPER Kconfig symbol.

Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com> #i915
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240704-panel-sw43408-fix-v6-1-3ea1c94bbb9b@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>