drm/i915/display: Use fixed_rr timings in modeset sequence

drm/i915/display: Use fixed_rr timings in modeset sequence

During modeset enable sequence, program the fixed timings, and turn on the
VRR Timing Generator (VRR TG) for platforms that always use VRR TG.

For this intel_vrr_set_transcoder now always programs fixed timings.
Later if vrr timings are required, vrr_enable() will switch
to the real VRR timings.

For platforms that will always use VRR TG, the VRR_CTL Enable bit is set
and reset in the transcoder enable/disable path.

v2: Update intel_vrr_set_transcoder_timings for fixed_rr.
v3: Update intel_set_transcoder_timings_lrr for fixed_rr. (Ville)
v4: Have separate functions to enable/disable VRR CTL
v5:
-For platforms that do not always have VRRTG on, do write bits other
than enable bit and also use write the TRANS_VRR_PUSH register. (Ville)
-Avoid writing trans_ctl_vrr if !vrr_possible().
v6:
-Disable VRR just before intel_ddi_disable_transcoder_func(). (Ville)
-Correct the sequence of configuring PUSH and VRR Enable/Disable. (Ville)
v7: Reset trans_vrr_ctl to 0 unconditionally in
intel_vrr_transcoder_disable(). (Ville)
v8: Reset trans_vrr_ctl if flipline is not set. (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/20250324133248.4071909-9-ankit.k.nautiyal@intel.com