vfio/ap: Move VFIODevice initializations in vfio_ap_instance_init

vfio/ap: Move VFIODevice initializations in vfio_ap_instance_init

Some of the VFIODevice initializations is in vfio_ap_realize,
move all of them in vfio_ap_instance_init.

No functional change intended.

Suggested-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>