usb: musb: sunxi: Add set_mode platform function

Move the mode handling to the platform_set_mode callback.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
[b-liu@ti.com: revise subject prefix]
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>