Hisilicon DSA Fabric device controller

Required properties:
- compatible: should be "hisilicon,hns-dsaf-v1" or "hisilicon,hns-dsaf-v2".
  "hisilicon,hns-dsaf-v1" is for hip05.
  "hisilicon,hns-dsaf-v2" is for Hi1610 and Hi1612.
- mode: dsa fabric mode string. only support one of dsaf modes like these:
		"2port-64vf",
		"6port-16rss",
		"6port-16vf",
		"single-port".
- interrupt-parent: the interrupt parent of this device.
- interrupts: should contain the DSA Fabric and rcb interrupt.
- reg: specifies base physical address(es) and size of the device registers.
  The first region is external interface control register base and size(optional,
  only be used when subctrl-syscon is not exists). It is recommended using
  subctrl-syscon rather than this address.
  The second region is SerDes base register and size(optional, only be used when
  serdes-syscon in port node is not exists. It is recommended using
  serdes-syscon rather than this address.
  The third region is the PPE register base and size.
  The fourth region is dsa fabric base register and size. It is not required for
  single-port mode.
- reg-names: may be ppe-base and(or) dsaf-base. It is used to find the
  corresponding reg's index.

- phy-handle: phy handle of physicl port, 0 if not any phy device. It is optional
  attribute. If port node is exists, phy-handle in each port node will be used.
  see ethernet.txt [1].
- subctrl-syscon: is syscon handle for external interface control register.
- reset-field-offset: is offset of reset field. Its value depends on the hardware
  user manual.
- buf-size: rx buffer size, should be 16-1024.
- desc-num: number of description in TX and RX queue, should be 512, 1024, 2048 or 4096.

- port: subnodes of dsaf. A dsaf node may contain several port nodes(Depending
  on mode of dsaf). Port node contain some attributes listed below:
- port-id: is physical port index in one dsaf.
- phy-handle: phy handle of physicl port. It is not required if there isn't
  phy device. see ethernet.txt [1].
- serdes-syscon: is syscon handle for SerDes register.
- cpld-syscon: is syscon handle for cpld register. It is not required if there
  isn't cpld device.
- cpld-ctrl-reg: is cpld register offset. It is not required if there isn't
  cpld-syscon.
- port-rst-offset: is offset of reset field for each port in dsaf. Its value
  depends on the hardware user manual.
- port-mode-offset: is offset of port mode field for each port in dsaf. Its
  value depends on the hardware user manual.

[1] Documentation/devicetree/bindings/net/phy.txt

Example:

dsaf0: dsa@c7000000 {
	compatible = "hisilicon,hns-dsaf-v1";
	mode = "6port-16rss";
	interrupt-parent = <&mbigen_dsa>;
	reg = <0x0 0xc5000000 0x0 0x890000
	       0x0 0xc7000000 0x0 0x60000>;
	reg-names = "ppe-base", "dsaf-base";
	subctrl-syscon = <&subctrl>;
	reset-field-offset = 0;
	interrupts = <131 4>,<132 4>, <133 4>,<134 4>,
		     <135 4>,<136 4>, <137 4>,<138 4>,
		     <139 4>,<140 4>, <141 4>,<142 4>,
		     <143 4>,<144 4>, <145 4>,<146 4>,
		     <147 4>,<148 4>, <384 1>,<385 1>,
		     <386 1>,<387 1>, <388 1>,<389 1>,
		     <390 1>,<391 1>,
	buf-size = <4096>;
	desc-num = <1024>;
	dma-coherent;

	prot@0 {
		port-id = 0;
		phy-handle = <&phy0>;
		serdes-syscon = <&serdes>;
	};

	prot@1 {
                port-id = 1;
                serdes-syscon = <&serdes>;
        };
};