usb: misc: usb3503: Add to select the ports to disable

This patch is to disable the USB ports unconnected to USB3503. In order to
disable the port, 'port_off_mask' must be set.

* Disable PORT1 only
	.port_off_mask = USB3503_OFF_PORT1;

* Disable PORT1 and PORT3 only
	.port_off_mask = USB3503_OFF_PORT1 | USB3503_OFF_PORT3;

* Enables all ports
	.port_off_mask = 0;

Signed-off-by: Dongjin Kim <tobetter@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>