dt-bindings: Add vendor prefix for LG Display

LG Display is an LCD display manufacturer. Originally formed as a joint
venture by LG Electronics and Philips Electronics, it was formerly known
as LG.Philips LCD, hence the DT vendor prefix lgphilips (which is
already in active use in the kernel).

More information is available at
https://en.wikipedia.org/wiki/LG_Display.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190813201101.30980-2-laurent.pinchart@ideasonboard.com