drm/i915/dp_mst: Use VRR Timing generator for DP MST for fixed_rr

drm/i915/dp_mst: Use VRR Timing generator for DP MST for fixed_rr

Currently the variable timings are supported only for DP and eDP and not
for DP MST. Call intel_vrr_compute_config() for MST which will configure
fixed refresh rate timings irrespective of whether VRR is supported or
not. Since vrr_capable still doesn't have support for DP MST this will be
just treated as non VRR case and vrr.vmin/vmax/flipline will be all set
to adjusted_mode->crtc_vtotal.

This will help to move away from the legacy timing generator and
always use VRR timing generator by default.

With this change, we need to exclude MST in intel_vrr_is_capable for
now, to avoid having LRR with MST.

v2: Exclude MST in intel_vrr_is_capable() for now. (Ville)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20250324133248.4071909-3-ankit.k.nautiyal@intel.com