usb: otg: mv_otg: Add dependence

This otg driver depends on marvell EHCI driver, so add the dependence.
It can fix the following build error on i386:

ERROR: "usb_remove_hcd" [drivers/usb/otg/mv_otg.ko] undefined!
ERROR: "usb_add_hcd" [drivers/usb/otg/mv_otg.ko] undefined!

Signed-off-by: Neil Zhang <zhangwm@marvell.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>