ARM: dts: rockchip: move edp-hpd pin definition into common location

The edp hotplug pin is fixed on the soc side, anybody wanting to use it
will need the same definition anyway, so move it to a common location.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Douglas Anderson <dianders@chromium.org>