LU-666 mdd depends on ldiskfs-only dynlocks feature

LU-666 mdd depends on ldiskfs-only dynlocks feature

As discussed in Lustre bugzilla 22435 dynlocks are provided by
the ldiskfs and are not a generic facility.  They should be
removed from the mdd-level to allow building --without-ldiskfs
per Andreas's comment in 22435:

  https://bugzilla.lustre.org/show_bug.cgi?id=22435#c3

This change converts the instances of "struct dynlock_handle *"
to a "void *" pointer which is safe because they are never
dereferenced at this level.

It also wraps the "struct dynlock" entry in the mdd_object with
MDD_DISABLE_PDO_LOCK.  This effectively limits all direct dynlock
usage to the !MDD_DISABLE_PDO_LOCK case which is unconditionally
disabled in the code.  Presumable this code will simply be removed
at some point which will fully resolve the issue.

Change-Id: I7c8d2fb04b31736782e5f6ea2ff6b631b475fb91
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-on: http://review.whamcloud.com/1348
Reviewed-by: wangdi <di.wang@whamcloud.com>
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>