usb: hub: port: add sysfs entry to switch port power

In some cases the port of an hub needs to be disabled or switched off
and on again. E.g. when the connected device needs to be re-enumerated.
Or it needs to be explicitly disabled while the rest of the usb tree
stays working.

For this purpose this patch adds an sysfs switch to enable/disable the
port on any hub. In the case the hub is supporting power switching, the
power line will be disabled to the connected device.

When the port gets disabled, the associated device gets disconnected and
removed from the logical usb tree. No further device will be enumerated
on that port until the port gets enabled again.

Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20220607114522.3359148-1-m.grzeschik@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>