USB: use PM core routines to enable/disable autosuspend

This patch (as1366) replaces the private routines
usb_enable_autosuspend() and usb_disable_autosuspend() with calls to
the standard pm_runtime_allow() and pm_runtime_forbid() functions in
the runtime PM framework.  They do the same thing.

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