vfio: Move vfio-region.h under hw/vfio/

Since the removal of vfio-platform, header file vfio-region.h no
longer needs to be a public VFIO interface. Move it under hw/vfio.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250901064631.530723-9-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

diff --git a/include/hw/vfio/vfio-region.h b/hw/vfio/vfio-region.h
similarity index 100%
rename from include/hw/vfio/vfio-region.h
rename to hw/vfio/vfio-region.h