vfio: Move VFIOAddressSpace helpers into container-base.c

vfio: Move VFIOAddressSpace helpers into container-base.c

VFIOAddressSpace is a common object used by VFIOContainerBase which is
declared in "hw/vfio/vfio-container-base.h". Move the VFIOAddressSpace
related services into "container-base.c".

While at it, rename :

  vfio_get_address_space -> vfio_address_space_get
  vfio_put_address_space -> vfio_address_space_put

to better reflect the namespace these routines belong to.

Reviewed-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Link: https://lore.kernel.org/qemu-devel/20250326075122.1299361-15-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>