drm/i915/dsi: Track the detailed DSC slice configuration

drm/i915/dsi: Track the detailed DSC slice configuration

Add tracking for the DSI DSC pipes-per-line and slices-per-stream value
in the slice config state and compute the current slices-per-line value
using this slice config state. The slices-per-line value used atm will
be removed by a follow-up change after converting all the places using
it to use the detailed slice config instead.

Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260114162232.92731-5-imre.deak@intel.com