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".
- 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.
  The second region is SerDes base register and size.
  The third region is the PPE register base and size.
  The fourth region is dsa fabric base register and size.
  The fifth region is cpld base register and size, it is not required if do not use cpld.
- phy-handle: phy handle of physicl port, 0 if not any phy device. see ethernet.txt [1].
- 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.

[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 0xC0000000 0x0 0x420000
	       0x0 0xC2000000 0x0 0x300000
	       0x0 0xc5000000 0x0 0x890000
	       0x0 0xc7000000 0x0 0x60000>;
	phy-handle = <0 0 0 0 &soc0_phy4 &soc0_phy5 0 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;
};