runtime: Introduce "vfio_mode" config variable and annotation

In order to support DPDK workloads, we need to change the way VFIO devices
will be handled in Kata containers.  However, the current method, although
it is not remotely OCI compliant has real uses.  Therefore, introduce a new
runtime configuration field "vfio_mode" to control how VFIO devices will be
presented to the container.

We also add a new sandbox annotation -
io.katacontainers.config.runtime.vfio_mode - to override this on a
per-sandbox basis.

For now, the only allowed value is "guest-kernel" which refers to the
current behaviour where VFIO devices added to the container will be bound
to whatever driver in the VM kernel claims them.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

src/runtime/virtcontainers/sandbox.go

@@ -134,6 +134,8 @@ type SandboxConfig struct {
 
 	ShmSize uint64
 
+	VfioMode config.VFIOModeType
+
 	// SharePidNs sets all containers to share the same sandbox level pid namespace.
 	SharePidNs bool