lwp: Don't depend on RX locking macros

lwp: Don't depend on RX locking macros

The lwp library should be independent of RX (in fact, bits of it are
a dependency for RX). So, LWP cannot use the MUTEX_ENTER, CV_WAIT, and
so on macros that RX defines.

Just implement these natively within the pthreaded bits of lock.c to
remove the dependency.

Change-Id: I4cdb8313e791f253e84bbc4e256087e46a4c59bd
Reviewed-on: http://gerrit.openafs.org/5396
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>