vhost: split out vringh Kconfig

vringh is pulled in by caif and mic, but the other
vhost config does not need to be there.
In particular, it makes no sense to have vhost net/scsi/sock
under caif/mic.

Create a separate Kconfig file and put vringh bits there.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/drivers/vhost/Kconfig.vringh b/drivers/vhost/Kconfig.vringh
new file mode 100644
index 0000000..6a4490c
--- /dev/null
+++ b/drivers/vhost/Kconfig.vringh
@@ -0,0 +1,5 @@
+config VHOST_RING
+	tristate
+	---help---
+	  This option is selected by any driver which needs to access
+	  the host side of a virtio ring.