drm/i915: Respect VBT seamless DRRS min refresh rate

Make sure our choice of downclock mode respects the VBT
seameless DRRS min refresh rate limit.

v2: s/vrefesh/vrefresh/ (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504150440.13748-10-ville.syrjala@linux.intel.com