vfio: mark posted writes in region write callbacks

For vfio-user, the region write implementation needs to know if the
write is posted; add the necessary plumbing to support this.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250607001056.335310-5-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
5 files changed