vop: pull in vhost Kconfig

VOP selects VHOST_RING. Pull in Kconfig that includes it
to make it self-containing.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/misc/mic/Kconfig

@@ -146,3 +146,7 @@ config VOP
 	  More information about the Intel MIC family as well as the Linux
 	  OS and tools for MIC to use with this driver are available from
 	  <http://software.intel.com/en-us/mic-developer>.
+
+if VOP
+source "drivers/vhost/Kconfig"
+endif