drm/i915/display: Introduce transcoder_has_vrr() helper

Introduce a new helper to check transcoder_has_vrr() and use
that to exclude transcoders which do not support VRR.

v2: Include HAS_VRR into the helper. (Ville)
v3: Drop the usage in places where not applicable. (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/20250327144629.648306-2-ankit.k.nautiyal@intel.com