pci: call hotplug callback even when not hotplug case for later use.

call hotplug callback even when not hotplug case for later use.
And move hotplug check into hotplug callback.
PCIE slot needs this for card presence detection.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
