libceph, ceph: add __init attribution to init funcitons

Add __init attribution to the functions which are called only once
during initiating/registering operations and deleting unnecessary
symbol exports.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>