ehci-hub: improved over-current recovery

According to the USB Specification Revision 2.0 chapter 11.12.5
a hub experiencing an over-current condition must place all
affected ports in the powered-off state. It seems that some root
hubs need port power to be cycled by software in order to get back
to normal functionality after an over-current condition ... like
the EHCI implementation on an MPC8343E.

Signed-off-by: Christian Engelmayer <christian.engelmayer@frequentis.com>
Signed-off-by: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>