Add opr/lock.h and tidy locking macros

Add opr/lock.h and tidy locking macros

The MUTEX_* and CV_* macros leaked from RX a while ago - they mean
that most of the pthreaded tree has a dependency on RX, as well as
further confusing the difference between userspace and kernel.

Tidy all of this up so that we have opr_mutex_* and opr_cv_* macros
to handle portable locking, and use these throughout the userspace
tree. Only kernel code should now use MUTEX_* and CV_*.

Provide opr/lockstub.h as a header that can be used by non-pthreaded
code to easily stub out these functions.

Change-Id: I24be525c7667641134d50561ce7f1e2d752cdf1f
Reviewed-on: http://gerrit.openafs.org/8280
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>