vdpa/ifc: support vring update after device config

vdpa/ifc: support vring update after device config

The device ready state in vhost lib is now defined as the state
that first queue pair is ready. And kick/callfd may be updated
by QEMU when ifc device is configured.

Although now ifc driver only supports one queue pair, it still
has to update callfd when working with QEMU. This patch fixes
this vring update problem by implementing the set_vring_state
callback.

Suggested-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Chenbo Xia <chenbo.xia@intel.com>
Acked-by: Xiao Wang <xiao.w.wang@intel.com>
Acked-by: Rosen Xu <rosen.xu@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>