USB: consolidate remote wakeup routines

This patch (as1324) makes a small change to the code used for remote
wakeup of root hubs.  hcd_resume_work() now calls the hub driver's
remote-wakeup routine instead of implementing its own version.

The patch is complicated by the need to rename remote_wakeup() to
usb_remote_wakeup(), make it non-static, and declare it in a header
file.  There's also the additional complication required to make
everything work when CONFIG_PM isn't set; the do-nothing inline
routine had to be moved into the header file.

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