drm/i915/dp: Simplify computing the DSC compressed BPP for DP-MST

drm/i915/dp: Simplify computing the DSC compressed BPP for DP-MST

The minimum/maximum DSC input (i.e. pipe) and compressed (i.e. link) BPP
limits are computed already in intel_dp_compute_config_limits(), so
there is no need to do this again in
mst_stream_dsc_compute_link_config() called later. Remove the
corresponding alignments from the latter function and use the
precomputed (aligned and within bounds) maximum pipe BPP and the min/max
compressed BPP values instead as-is.

Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20251222153547.713360-21-imre.deak@intel.com