ocfs2: clean up mount option about atime in ocfs2.txt

As ocfs2 supports relatime and strictatime, we need update the
relative document. Atime_quantum need work with strictatime, so only
show it in procfs when mount with strictatime.

Signed-off-by: Tiger Yang <tiger.yang@oracle.com>
Signed-off-by: Joel Becker <jlbec@evilplan.org>