* USB2 ChipIdea USB controller for ci13xxx

Required properties:
- compatible: should be "chipidea,usb2"
- reg: base address and length of the registers
- interrupts: interrupt for the USB controller

Optional properties:
- clocks: reference to the USB clock
- phys: reference to the USB PHY
- phy-names: should be "usb-phy"
- vbus-supply: reference to the VBUS regulator
- maximum-speed: limit the maximum connection speed to "full-speed".
- tpl-support: TPL (Targeted Peripheral List) feature for targeted hosts
- itc-setting: interrupt threshold control register control, the setting
  should be aligned with ITC bits at register USBCMD.
- ahb-burst-config: it is vendor dependent, the required value should be
  aligned with AHBBRST at SBUSCFG, the range is from 0x0 to 0x7. This
  property is used to change AHB burst configuration, check the chipidea
  spec for meaning of each value. If this property is not existed, it
  will use the reset value.
- tx-burst-size-dword: it is vendor dependent, the tx burst size in dword
  (4 bytes), This register represents the maximum length of a the burst
  in 32-bit words while moving data from system memory to the USB
  bus, the value of this property will only take effect if property
  "ahb-burst-config" is set to 0, if this property is missing the reset
  default of the hardware implementation will be used.
- rx-burst-size-dword: it is vendor dependent, the rx burst size in dword
  (4 bytes), This register represents the maximum length of a the burst
  in 32-bit words while moving data from the USB bus to system memory,
  the value of this property will only take effect if property
  "ahb-burst-config" is set to 0, if this property is missing the reset
  default of the hardware implementation will be used.
- extcon: phandles to external connector devices. First phandle should point to
  external connector, which provide "USB" cable events, the second should point
  to external connector device, which provide "USB-HOST" cable events. If one
  of the external connector devices is not required, empty <0> phandle should
  be specified.
- phy-clkgate-delay-us: the delay time (us) between putting the PHY into
  low power mode and gating the PHY clock.
- non-zero-ttctrl-ttha: after setting this property, the value of register
  ttctrl.ttha will be 0x7f; if not, the value will be 0x0, this is the default
  value. It needs to be very carefully for setting this property, it is
  recommended that consult with your IC engineer before setting this value.
  On the most of chipidea platforms, the "usage_tt" flag at RTL is 0, so this
  property only affects siTD.
  If this property is not set, the max packet size is 1023 bytes, and if
  the total of packet size for pervious transactions are more than 256 bytes,
  it can't accept any transactions within this frame. The use case is single
  transaction, but higher frame rate.
  If this property is set, the max packet size is 188 bytes, it can handle
  more transactions than above case, it can accept transactions until it
  considers the left room size within frame is less than 188 bytes, software
  needs to make sure it does not send more than 90%
  maximum_periodic_data_per_frame. The use case is multiple transactions, but
  less frame rate.

i.mx specific properties
- fsl,usbmisc: phandler of non-core register device, with one
  argument that indicate usb controller index
- disable-over-current: disable over current detect
- external-vbus-divider: enables off-chip resistor divider for Vbus

Example:

	usb@f7ed0000 {
		compatible = "chipidea,usb2";
		reg = <0xf7ed0000 0x10000>;
		interrupts = <GIC_SPI 11 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&chip CLKID_USB0>;
		phys = <&usb_phy0>;
		phy-names = "usb-phy";
		vbus-supply = <&reg_usb0_vbus>;
		gadget-itc-setting = <0x4>; /* 4 micro-frames */
		 /* Incremental burst of unspecified length */
		ahb-burst-config = <0x0>;
		tx-burst-size-dword = <0x10>; /* 64 bytes */
		rx-burst-size-dword = <0x10>;
	};