drm/i915/vrr: Always use VRR timing generator for PTL+

drm/i915/vrr: Always use VRR timing generator for PTL+

Currently, the VRR timing generator is used only when VRR is enabled by
userspace for sinks that support VRR. Starting with PTL+, gradually move
away from the legacy timing generator and use the VRR timing generator
for both variable and fixed timings.

Note: For platforms where we always enable the VRR timing generator,
the LRR fastset is not allowed to avoid live programming of vrr.guardband
with VRR TG enabled. This effectively breaks the LRR fastset functionality
for these platforms and needs to be addressed.

v2: Use this for PTL for now to avoid losing LRR fastset for older
platforms. (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/20250324133248.4071909-14-ankit.k.nautiyal@intel.com