USB: speed up usb_bus_resume()

This patch (as1620) speeds up USB root-hub resumes in the common case
where every enabled port has its suspend feature set (which currently
will be true for every runtime resume of the root hub).  If all the
enabled ports are suspended then resuming the root hub won't resume
any of the downstream devices.  In this case there's no need for a
Resume Recovery delay, because that delay is meant to give devices a
chance to get ready for active use.

To keep track of the port suspend features, the patch adds a
"port_is_suspended" flag to struct usb_device.  This has to be tracked
separately from the device's state; it's entirely possible for a USB-2
device to be suspended while the suspend feature on its parent port is
clear.  The reason is that devices will go into suspend whenever their
parent hub does.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reviewed-by: Peter Chen <peter.chen@freescale.com>
Tested-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>