drm/i915: Check the LID device to decide whether the LVDS should be initialized

On some boxes the mobile chipset is used and there is no LVDS device. In such
case we had better not initialize the LVDS output device so that one pipe can
be used for other output device. For example: E-TOP.

But unfortunately the LVDS device is still initialized on the boxes based on
mobile chipset in KMS mode. It brings that this pipe occupied by LVDS can't be
used for other output device.

After checking the acpidump we find that there is no LID device on such boxes.
In such case we can use the LID device to decide whether the LVDS device should
be initialized.

If there is no LID device, we can think that there is no LVDS device. It is
unnecessary to initialize the LVDS output device.
If there exists the LID device, it will continue the current flowchart.

Maybe on some boxes there is no LVDS device but the LID device is found. In
such case it should be added to the quirk list.

http://bugs.freedesktop.org/show_bug.cgi?id=21496
http://bugs.freedesktop.org/show_bug.cgi?id=21856
http://bugs.freedesktop.org/show_bug.cgi?id=21127



Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[anholt: squashed in style fixups]
Signed-off-by: Eric Anholt <eric@anholt.net>