Revert "ocfs2: change ip_unaligned_aio to of type mutex from atomit_t"

Revert "ocfs2: change ip_unaligned_aio to of type mutex from atomit_t"

This reverts commit c18ceab01240fd4c354b78d877571b729908e4a3.

Test shows ip_unaligned_aio will cost much cpu clock when doing aio+dio(in a
function named mutex_spin_on_owner), and will significant affect performance in
a system with poor cpu.

The cause is we should not call mutex_unlock(see the comments above
mutex_unlock) in ocfs2_dio_end_io, which will be in irq context when doing
aio+dio.

Revert the patch to use wait_event/wake_up_all to do the work.

Signed-off-by: Ryan Ding <ryan.ding@oracle.com>
Reviewed-by: Junxiao Bi <junxiao.bi@oracle.com>