drm/i915: generate a KMS uevent at lid open/close time

With all the other lid pieces in place, it's easy to generate a uevent
for the LVDS connector just like we do for other outputs.  Should make
lid open/close fit in with the rest of a userland based output
reconfiguration scheme.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>