drm/i915/dp: Account for DSC slice overhead

drm/i915/dp: Account for DSC slice overhead

Account for DSC slice overhead bubbles and adjust the pixel rate while
checking the pixel rate against the max dotclock limits.

v2: Add missing assignment for dsc_slice_count in
mst_connector_mode_valid_ctx(). (Imre)

v3: Explicitly pass dsc_slice_count as 0 for Non-DSC case. (Imre)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260202103731.357416-15-ankit.k.nautiyal@intel.com