Bluetooth: Enable USB autosuspend by default on btusb

We've done this for a while in Fedora without any obvious problems other
than some interaction with input devices. Those should be fixed now, so
let's try this in mainline.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>