HACK: board: vim3: reset usb controller upon system reset

On the VIM3L board, with some USB cables/hosts, there is a long (5s)
delay before between "fastboot reboot" and the host detecting a USB
reset.

This breaks tools relying on "fastboot reboot fastboot" which assume
that 1s after the command send, the board should disconnect on usb.

To reproduce, enable fastboot in U-Boot console:
=> fastboot usb 0

Then, on the host, run:
  # echo "running fastboot reboot bootloader" > /dev/kmsg && fastboot reboot bootloader
  Rebooting into bootloader                          OKAY [  0.003s]
  Finished. Total time: 3.033s

  [54074.251551] running fastboot reboot bootloader
  ... there is a delay of 5s before we detect a disconnection ...
  [54079.041238] usb 1-7.4: USB disconnect, device number 72
  [54079.239625] usb 1-7.4: new high-speed USB device number 73 using xhci_hcd
  [54079.359103] usb 1-7.4: New USB device found, idVendor=1b8e, idProduct=fada, bcdDevice= 2.27
  [54079.359110] usb 1-7.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
  [54079.359112] usb 1-7.4: Product: USB download gadget
  [54079.359114] usb 1-7.4: Manufacturer: U-Boot
  [54079.359116] usb 1-7.4: SerialNumber: C8631470CC41

Note: this does not happen when we use the RST button on the board, nor in linux.

Resetting the usb controller before psci_reset fixes this.

Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>