usb: musb: da8xx: Set phy in OTG mode by default

The DA8xx OTG PHY has some issues when it is forced in host or
peripheral mode. Actually, most of the time, OTG is the best mode
because host or peripheral mode are only required for hardware that
miss some circuitry.
Init the PHY mode OTG mode by default.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>