Altera SOCFPGA SoC DWMAC controller

This is a variant of the dwmac/stmmac driver an inherits all descriptions
present in Documentation/devicetree/bindings/net/stmmac.txt.

The device node has additional properties:

Required properties:
 - compatible	: For Cyclone5/Arria5 SoCs it should contain
		  "altr,socfpga-stmmac". For Arria10/Agilex/Stratix10 SoCs
		  "altr,socfpga-stmmac-a10-s10".
		  Along with "snps,dwmac" and any applicable more detailed
		  designware version numbers documented in stmmac.txt
 - altr,sysmgr-syscon : Should be the phandle to the system manager node that
   encompasses the glue register, the register offset, and the register shift.
   On Cyclone5/Arria5, the register shift represents the PHY mode bits, while
   on the Arria10/Stratix10/Agilex platforms, the register shift represents
   bit for each emac to enable/disable signals from the FPGA fabric to the
   EMAC modules.
 - altr,f2h_ptp_ref_clk use f2h_ptp_ref_clk instead of default eosc1 clock
   for ptp ref clk. This affects all emacs as the clock is common.

Optional properties:
altr,emac-splitter: Should be the phandle to the emac splitter soft IP node if
		DWMAC controller is connected emac splitter.
phy-mode: The phy mode the ethernet operates in
altr,sgmii-to-sgmii-converter: phandle to the TSE SGMII converter

This device node has additional phandle dependency, the sgmii converter:

Required properties:
 - compatible	: Should be altr,gmii-to-sgmii-2.0
 - reg-names	: Should be "eth_tse_control_port"

Example:

gmii_to_sgmii_converter: phy@100000240 {
	compatible = "altr,gmii-to-sgmii-2.0";
	reg = <0x00000001 0x00000240 0x00000008>,
		<0x00000001 0x00000200 0x00000040>;
	reg-names = "eth_tse_control_port";
	clocks = <&sgmii_1_clk_0 &emac1 1 &sgmii_clk_125 &sgmii_clk_125>;
	clock-names = "tse_pcs_ref_clk_clock_connection", "tse_rx_cdr_refclk";
};

gmac0: ethernet@ff700000 {
	compatible = "altr,socfpga-stmmac", "snps,dwmac-3.70a", "snps,dwmac";
	altr,sysmgr-syscon = <&sysmgr 0x60 0>;
	reg = <0xff700000 0x2000>;
	interrupts = <0 115 4>;
	interrupt-names = "macirq";
	mac-address = [00 00 00 00 00 00];/* Filled in by U-Boot */
	clocks = <&emac_0_clk>;
	clock-names = "stmmaceth";
	phy-mode = "sgmii";
	altr,gmii-to-sgmii-converter = <&gmii_to_sgmii_converter>;
};
