vhost: move linux virtio headers to include/

These headers are needed on systems that have old
kernels without virtio_scsi.h and virtio_types.h.
Move them out of the vhost directory and into include
so that they can be used by an upcoming virtio-scsi
initiator bdev module.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ie6614b8845568729a38665c4c1a366b97978e315

Reviewed-on: https://review.gerrithub.io/374548


Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>