pci: do not export pci_bus_reset

qbus_reset_all can be used instead.  There is no semantic change
because pcibus_reset returns 1 and takes care of the device
tree traversal.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
