drm/i915: use ACPI LID status for LVDS ->detect hook

We can't load or hotplug detect LVDS like we can other outputs, but if
there's a lid device present we can use it as a proxy.  This allows the
LFP state to be determined at ->detect time, making configurations
requiring manual intervention today "just work" assuming the lid device
status is correct.

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