drm/i915/lvds: simplify gen 2 lvds presence

Gen 2 mobile and not I830 is, in fact, I85X. Simplify.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190122082307.4003-6-jani.nikula@intel.com