drm/i915/vrr: Introduce intel_vrr_vblank_delay()

Introduce a VRR specific function for determining the current
vblank delay. Currently thus will give the same answer as
intel_mode_vblank_delay() but that will change later.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241210211007.5976-13-ville.syrjala@linux.intel.com


Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>