dt-bindings: Add vendor prefix for kingdisplay

Kingdisplay Technology Co., Ltd, established in
China Shenzhen in 2006, is a national high-tech
enterprise specializing in the R&D, manufacturing
and marketing of TFT-LCM and touch panel.

Signed-off-by: Nickey Yang <nickey.yang@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180702103229.3952-2-heiko@sntech.de