USB: pxa27x_udc: add otg transceiver support

When a transceiver driver is used, no automatic udc enable
is done. The transceiver (OTG or not) should :
 - take care of VBus sensing
 - call usb_gadget_vbus_connect()
 - call usb_gadget_vbus_disconnect()

The pullup should remain within this driver's management,
either by gpio_pullup of udc_command() fields.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>