vfio/vfio-container-base.h: update VFIOContainerBase declaration

vfio/vfio-container-base.h: update VFIOContainerBase declaration

Update the VFIOContainerBase declaration to match our current coding
guidelines: remove the explicit typedef (this is already handled by the
OBJECT_DECLARE_TYPE() macro), add a blank line after the parent object,
rename parent to parent_obj, and move the macro declaration next to the
VFIOContainerBase struct declaration.

Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250715093110.107317-2-mark.caveayland@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>