net: gmac_rockchip: Add support for the RV1108 GMAC

net: gmac_rockchip: Add support for the RV1108 GMAC

The rv1108 GMAC only support rmii interface, so need to add the
set_rmii() ops. Use the phy current interface to set rmii or
rgmii ops. At the same time, need to set the mac clock rate of
rmii with 50M, the clock rate of rgmii with 125M.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>