arm: juno: enable USB

The Juno board features a standard compliant EHCI/OHCI USB host
controller pair, which we can just enable.
The platform data is taken from the device tree.

This allows to use USB mass storage (the only storage on a Juno r0)
for loading.

At least on my board USB seems a bit flaky, I need two "usb reset"
sequences after the "usb start" to detect an USB hard drive.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>