drm/i915/vrr: Refactor condition for computing vmax and LRR

drm/i915/vrr: Refactor condition for computing vmax and LRR

LRR and Vmax can be computed only if VRR is supported and vrr.in_range
is set. Currently we proceed with vrr timings only for VRR supporting
panels and return otherwise. For using VRR TG with fix timings, need to
continue even for panels that do not support VRR.

To achieve this, refactor the condition for computing vmax and
update_lrr so that we can continue for fixed timings for panels that do
not support VRR.

v2: Set vmax = vmin for non VRR panels. (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/20250324133248.4071909-6-ankit.k.nautiyal@intel.com