PCI: hotplug: pciehp: wait for 1 second after power off slot

According to the specification, we must wait for at least 1 second
after turning power off before taking any action that relies on power
having been removed from the slot/adapter.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>