hw/9pfs: Improve portability to older systems

handle fs driver require a set of newly added syscalls. Don't
Compile handle FS driver if those syscalls are not available.
Instead of adding #ifdef for all those syscalls we check for
open by handle syscall. If that is available then rest of the
syscalls used by the driver should be available.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

fsdev/qemu-fsdev.c

@@ -23,7 +23,9 @@ static QTAILQ_HEAD(FsDriverEntry_head, FsDriverListEntry) fsdriver_entries =
 
 static FsDriverTable FsDrivers[] = {
     { .name = "local", .ops = &local_ops},
+#ifdef CONFIG_OPEN_BY_HANDLE
     { .name = "handle", .ops = &handle_ops},
+#endif
     { .name = "synth", .ops = &synth_ops},
 };