usb: gadget: mv_udc: use udc_start and udc_stop functions

This patches converts the driver into the new style start/stop
interface. As a result the driver no longer uses the static
global the_conroller variable.

Signed-off-by: Chao Xie <chao.xie@marvell.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>