dt-bindings: net: dwmac: Add Rockchip DWMAC support

Add Rockchip DWMAC controllers, which are based on snps,dwmac.
Some of the SoCs require up to eight clocks, so maxItems
for clocks and clock-names need to be increased.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: David S. Miller <davem@davemloft.net>