drm/dp: Add drm_dp_dsc_sink_slice_count_mask()

drm/dp: Add drm_dp_dsc_sink_slice_count_mask()

A DSC sink supporting DSC slice count N, not necessarily supports slice
counts less than N. Hence the driver should check the sink's support for
a particular slice count before using that slice count. Add the helper
functions required for this.

Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20251215192357.172201-3-imre.deak@intel.com