USB: export autosuspend delay in sysfs

This patch (as861) adds sysfs attributes to expose the autosuspend
delay value for each USB device.  If the user changes the delay from 0
(no autosuspend) to a positive value, an autosuspend is attempted.

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