ehci-platform: Add support for controllers with big-endian regs / descriptors

This uses the already documented devicetree booleans for this, see:
Documentation/devicetree/bindings/usb/usb-ehci.txt

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>