convert file+pipe chardevs to QemuOpts.

new cmd line syntax:
    -chardev file,id=name,path=/path/to/file
    -chardev pipe,id=name,path=/path/to/pipe

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-config.c

@@ -79,6 +79,13 @@ QemuOptsList qemu_chardev_opts = {
     .name = "chardev",
     .head = TAILQ_HEAD_INITIALIZER(qemu_chardev_opts.head),
     .desc = {
+        {
+            .name = "backend",
+            .type = QEMU_OPT_STRING,
+        },{
+            .name = "path",
+            .type = QEMU_OPT_STRING,
+        },
         { /* end if list */ }
     },
 };