dt-bindings: net: Add the properties for ipq4019 MDIO

The new added properties resource "reg" is for configuring
ethernet LDO in the IPQ5018 chipset, the property "clocks"
is for configuring the MDIO clock source frequency.

Signed-off-by: Luo Jie <luoj@codeaurora.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>