ATH79 USB EHCI controllers

Required properties:
  - compatible : should be "qca, ath79-ehci".
  - reg : should contain at least address and length of the standard EHCI
    register set for the device. Optional platform-dependent registers
    (debug-port or other) can be also specified here, but only after
    definition of standard EHCI registers.
  - interrupts : one EHCI interrupt should be described here.

Optional properties:
 - big-endian-regs : boolean, set this for hcds with big-endian registers
 - big-endian-desc : boolean, set this for hcds with big-endian descriptors
 - big-endian : boolean, for hcds with big-endian-regs + big-endian-desc
 - needs-reset-on-resume : boolean, set this to force EHCI reset after resume
 - has-transaction-translator : boolean, set this if EHCI have a Transaction
				Translator built into the root hub.
 - clocks : a list of phandle + clock specifier pairs
 - phys : phandle + phy specifier pair
 - phy-names : "usb"
 - resets : phandle + reset specifier pair
 - qca_force_host_mode: Set, if host mode to be forced for ATH79 SoCs
 - qca_force_16bit_ptw: Set, if 16bit ptw to be forced for ATH79 SoCs
 - caps-offset: Specify the caps offset

Example (Qualcomm Atheros ATH79 SoC)

   ehci0: usb@1b000000 {
	   compatible = "qca,ath79-ehci", "qca,ap135-ehci", qca,ap137-ehci", "qca,ap147-ehci";
	   reg = <0x1b000000 0x200>;
	   interrupt-parent = <&ip3_int>;
	   interrupts = <0>;
	   has-transaction-translator;
	   qca_force_host_mode;
	   qca_force_16bit_ptw;
	   caps-offset = <0x100>;
	   status = "okay";
   };