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/qemu-config.c b/qemu-config.c
index 18f3020..1bdc01c 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -211,6 +211,9 @@
         }, {
             .name = "readonly",
             .type = QEMU_OPT_BOOL,
+        }, {
+            .name = "sock_fd",
+            .type = QEMU_OPT_NUMBER,
         },
 
         { /*End of list */ }
@@ -240,6 +243,9 @@
         }, {
             .name = "readonly",
             .type = QEMU_OPT_BOOL,
+        }, {
+            .name = "sock_fd",
+            .type = QEMU_OPT_NUMBER,
         },
 
         { /*End of list */ }