hw/9pfs: Add new proxy filesystem driver

Add new proxy filesystem driver to add root privilege to qemu process.
It needs a helper process to be started by root user.

Following command line can be used to utilize proxy filesystem driver
-virtfs proxy,id=<id>,mount_tag=<tag>,socket_fd=<socket-fd>

Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
diff --git a/fsdev/qemu-fsdev.c b/fsdev/qemu-fsdev.c
index 00f48ab..e20202a 100644
--- a/fsdev/qemu-fsdev.c
+++ b/fsdev/qemu-fsdev.c
@@ -27,6 +27,7 @@
     { .name = "handle", .ops = &handle_ops},
 #endif
     { .name = "synth", .ops = &synth_ops},
+    { .name = "proxy", .ops = &proxy_ops},
 };
 
 int qemu_fsdev_add(QemuOpts *opts)