HID: minimal autosuspend support for USB HID devices

Autosuspend for USB HID devices remains problematic as far as mice
and keyboards are concerned. While I am working on a grand solution,
here's a minimalist patch that works for those devices not continously
in use.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>