USB: ohci-pxa27x: Add support for external vbus regulators

Override the hub control operation to enable and disable external
regulators for the ports vbus power supply in response to clear/set
USB_PORT_FEAT_POWER requests.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>