vfio: Add header guards and includes to drivers/vfio/vfio.h

As is normal for headers.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/1-v3-297af71838d2+b9-vfio_container_split_jgg@nvidia.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>