usb: Deprecate the legacy -usbdevice option

usb: Deprecate the legacy -usbdevice option

The '-usbdevice' option is considered as deprecated nowadays and
we might want to remove these options in a future version of QEMU.
So mark this options as deprecated in the documenation and print out
a warning if it is used to tell the user what to use instead.
While we're at it, improve also some other minor USB-related spots
in qemu-options.hx that were not up to date anymore.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1495175716-12735-1-git-send-email-thuth@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>