usb: Make USB_MUSB_PIO_ONLY selected by USB_MUSB_SUNXI

This ensures the USB_MUSB_PIO_ONLY config is set to an apppropriate
value from the changes enabling USB_MUSB_GADGET does.

Namely, USB_MUSB_PIO_ONLY default to =y on USB_MUSB_SUNXI being y.

Signed-off-by: Samuel Dionne-Riel <samuel@dionne-riel.com>