drm/i915: Addin-offset is an unreliable indicator of LVDS presence (v2)

My Samsung N210 has a VBT with DEVICE_TYPE_INT_LFP with a zero
addin-offset. With the check in place, the panel was declared absent.

v2: Only trust BIOS writers that have graduated to writing OpRegions.
(We are all doomed.)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Cc: Adam Jackson <ajax@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>