virtio-9p: Create a syntactic shortcut for the file-system pass-thru

Currently the commandline to create a virtual-filesystem pass-through between
the guest and the host is as follows:
#qemu -fsdev fstype,id=ID,path=path/to/share \
      -device virtio-9p-pci,fsdev=ID,mount_tag=tag \

This patch provides a syntactic short-cut to achieve the same as follows:
#qemu -virtfs fstype,path=path/to/share,mount_tag=tag

This will be internally expanded as:
#qemu -fsdev fstype,id=tag,path=path/to/share, \
      -device virtio-9p-pci,fsdev=tag,mount_tag=tag \

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-config.c

@@ -169,6 +169,28 @@ QemuOptsList qemu_fsdev_opts = {
 };
 #endif
 
+#ifdef CONFIG_LINUX
+QemuOptsList qemu_virtfs_opts = {
+    .name = "virtfs",
+    .implied_opt_name = "fstype",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_virtfs_opts.head),
+    .desc = {
+        {
+            .name = "fstype",
+            .type = QEMU_OPT_STRING,
+        }, {
+            .name = "path",
+            .type = QEMU_OPT_STRING,
+        }, {
+            .name = "mount_tag",
+            .type = QEMU_OPT_STRING,
+        },
+
+        { /*End of list */ }
+    },
+};
+#endif
+
 QemuOptsList qemu_device_opts = {
     .name = "device",
     .implied_opt_name = "driver",