drm/i915/dsi: Move initialization of DSI DSC streams-per-pipe to fill_dsc()

drm/i915/dsi: Move initialization of DSI DSC streams-per-pipe to fill_dsc()

Move the initialization of the DSI DSC streams-per-pipe value to
fill_dsc() next to where the corresponding (per-line) slice_count value
is initialized. This allows converting the initialization to use the
detailed slice configuration state in follow-up changes.

Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260114162232.92731-4-imre.deak@intel.com