dt-bindings: display: rockchip-lvds: Remove panel references

The panel bindings are outside the scope of the Rockchip LVDS interface
binding. The references are about to change too, so rather than update
them just drop the section on the panel bindings.

Cc: Sandy Huang <hjc@rock-chips.com>
Cc: "Heiko Stübner" <heiko@sntech.de>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-rockchip@lists.infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20190624215649.8939-2-robh@kernel.org