ethernet: arc: Add support for Rockchip SoC layer device tree bindings

This patch defines a platform glue layer for Rockchip SoCs which
support arc-emac driver. It ensures that regulator for the rmii is on
before trying to connect to the ethernet controller. It applies right
speed and mode changes to the grf when ethernet settings change.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
dt-bindings: Document EMAC Rockchip

This adds the necessary binding documentation for the EMAC Rockchip platform
driver found in RK3066 and RK3188 SoCs.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
ARM: dts: Add emac nodes to the rk3188 device tree

This adds support for EMAC Rockchip driver on RK3188 SoCs.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
ARM: dts: Enable emac node on the rk3188-radxarock boards

This enables EMAC Rockchip support on radxa rock boards.

Signed-off-by: Romain Perier <romain.perier@gmail.com>