fsnotify: use _rcu functions for mark list traversal

In preparation for srcu locking use all _rcu appropiete functions for mark
list addition, removal, and traversal.  The operations are still done under a
spinlock at the end of this patch.

Signed-off-by: Eric Paris <eparis@redhat.com>

diff --cc fs/notify/inode_mark.c
Simple merge

diff --cc fs/notify/vfsmount_mark.c
Simple merge