wake_up_bit and wake_up_var are fragile interfaces as they sometimes
require a barrier before them.  Recently some new interfaces were added
which avoid the need for explicit barriers.  If we can remove all
instances of those fragile interfaces, that would be ideal.

Unforunately there is one can in NFS that does not fit the new
interfaces.  However most do.  This series replaces most use of the old
interfaces with the new, and adds various related cleanups.

Thanks,
NeilBrown