On MST links - at least for some MST branch devices - the list of modes
returned to users on an enabled link depends on the current link
rate/lane count parameters (besides the DPRX link capabilities, any MST
branch BW limit and the maximum link parameters reduced after LT
failures). In particular the MST branch BW limit may depend on the link
rate/lane count parameters programmed to DPCD. After an LT failure and
limiting the maximum link parameters accordingly, users should see a
mode list reflecting these new limits. However with the current fallback
order this isn't ensured, as the new limit could allow for modes
requiring a higher link BW, but these modes will be filtered out due to
the enabled link's lower link BW.

Ensure that the mode list changes in a consistent way after a link
training failure and reducing the link parameters by changing the
fallback order on MST links to happen in BW order.

v2:
- s/INTEL_DP_MAX_SUPPORTED_LANE_COUNTS/INTEL_DP_MAX_SUPPORTED_LANE_CONFIGS
  and s/num_common_lane_counts/num_common_lane_configs to make the
  difference wrt. max lane counts clearer. (Suraj)
- Add a TODO comment to make the SST fallback logic work the same way as
  MST. (Arun)
- Use sort_r()'s default swap function instead of a custom one.

Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240729144458.2763667-1-imre.deak@intel.com