Missing USB clock for BCM2835

[Stefan Wahren]

Hi,
i'm working on Raspberry Pi Zero support (incl. OTG / Gadget). I wanted to add
the missing clock control for DWC2 [1], but i didn't find a matching clock in
the clock tree.

The BCM2835 clk driver contains the define A2W_XOSC_CTRL_USB_ENABLE, but no
separate registers. So i assume USB clock is a child of xosc only with a gate
and a fixed frequency of 480 MHz.

Is it correct?

[1] -
http://lxr.free-electrons.com/source/Documentation/devicetree/bindings/usb/dwc2.txt