We need to dump content of some fs like binfmt_misc, tmpfs, ... To facilitate
this the existing list of filesystems is turned into an array of structures
with dump and restore callbacks. Each FS may declare them they need.

v2: rework encode/decode_fstype not to do it twice.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>