Now that the musb-new driver has a Kconfig, we can move Kconfig options to
enable controllers to it, so that it's easier in e.g. menuconfig.

In addition, this allows declaring support for USB_MUSB_HOST/GADGET in
defconfigs instead of the USB_MUSB_SUNXI controller, that will get selected
automatically when needed.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>