USB: expand autosuspend/autoresume API

This patch (as814) adds usb_autopm_set_interface() to the autosuspend
API.  It also provides convenient wrapper routines,
usb_autopm_enable() and usb_autopm_disable(), for drivers that want
to specify directly whether autosuspend should be allowed.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>