USB: serial: full autosuspend support for the option driver

this adds autosupport usable even in an always online mode.

- enables remote wakeup on open
- autoresume for sending
- timeout based autosuspend if nothing is sent or recieved
- autosuspend without remote wakeup support on open/close

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Tested-off-by: Zhao Ming <zhao.ming9@zte.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>