arm64: dts: rk3399: Remove extcon unit address and extcon-cells from Gru

The cros-ec-extcon has no reg property so remove the unit address from
the DT node to make DT compiler happy.

While here, remove the inexistent extcon-cells property from the extcon
nodes.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20200207141324.3188898-1-enric.balletbo@collabora.com


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