drm/i915/mst: adapt intel_dp_mtp_tu_compute_config() for 128b/132b SST

Handle 128b/132b SST in intel_dp_mtp_tu_compute_config(). The remote
bandwidth overhead and time slot allocation are only relevant for MST;
SST only needs the local bandwidth and a check that 64 slots isn't
exceeded.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b59c94b0aac2c073b0306c0a0040b26330f94260.1735912293.git.jani.nikula@intel.com