net: emaclite: Support multiple phys connected to one MDIO bus

For system which contains at least two ethernet IP where
one IP manage MDIO bus with several PHYs.

Example dts node:
ethernet_mac0: ethernet@81000000 {
	compatible = "xlnx,xps-ethernetlite-1.00.a";
	device_type = "network";
	interrupt-parent = <&xps_intc_0>;
	interrupts = < 1 0 >;
		local-mac-address = [ 00 0a 35 00 db bb ];
	phy-handle = <&ethernet_mac0_phy0>;
	reg = < 0x81000000 0x10000 >;
	xlnx,duplex = <0x1>;
	xlnx,family = "spartan3e";
	xlnx,include-internal-loopback = <0x0>;
	xlnx,include-mdio = <0x1>;
	xlnx,rx-ping-pong = <0x0>;
	xlnx,tx-ping-pong = <0x0>;
	ethernet_mac0_mdio {
		#address-cells = <1>;
		#size-cells = <0>;
		ethernet_mac0_phy0: phy@1 {
			reg = <0x1>;
		} ;
		ethernet_mac0_phy1: phy@3 {
			reg = <0x3>;
		} ;
	} ;
} ;
ethernet_mac2: ethernet@81040000 {
	compatible = "xlnx,xps-ethernetlite-1.00.a";
	device_type = "network";
	interrupt-parent = <&xps_intc_0>;
	interrupts = < 11 0 >;
		local-mac-address = [ 00 0a 35 00 db bb ];
	phy-handle = <&ethernet_mac0_phy1>;
	reg = < 0x81040000 0x10000 >;
	xlnx,duplex = <0x1>;
	xlnx,family = "spartan3e";
	xlnx,include-internal-loopback = <0x0>;
	xlnx,include-mdio = <0x0>;
	xlnx,rx-ping-pong = <0x0>;
	xlnx,tx-ping-pong = <0x0>;
} ;

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>