vhost-user: move VhostUserProtocolFeature definition to header file

vhost-user: move VhostUserProtocolFeature definition to header file

Move the definition of VhostUserProtocolFeature to
include/hw/virtio/vhost-user.h.

Remove previous definitions in hw/scsi/vhost-user-scsi.c,
hw/virtio/vhost-user.c, and hw/virtio/virtio-qmp.c.

Previously there were 3 separate definitions of this over 3 different
files. Now only 1 definition of this will be present for these 3 files.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
Reviewed-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-Id: <20230926224107.2951144-4-jonah.palmer@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>