ARM: dts: rockchip: move rk3288 edp phy under the GRF

The edp-phy control is a part of the General Register Files and
with a recent patch in 4.6 the phy driver can now also handle this
correctly, so move the dts node under the GRF as well.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>