drm/i915/dsc: Track the DSC stream count in the DSC slice config state

drm/i915/dsc: Track the DSC stream count in the DSC slice config state

Move the tracking for the DSC stream count from
intel_crtc_state::dsc.num_streams to
intel_crtc_state::dsc.slice_config.streams_per_pipe.

While at it add a TODO comment to read out the full DSC configuration
from HW including the pipes-per-line and slices-per-stream values.

Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260114162232.92731-3-imre.deak@intel.com