vfio_spapr_create_window calls vfio_spapr_remove_window,
With reoder of definition of the two, we can make
vfio_spapr_create/remove_window static.

No functional changes intended.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>