LU-4588 code: replace semaphores with mutexes

LU-4588 code: replace semaphores with mutexes

It's just optimization. The mutex subsystem is slightly faster
and has better scalability for contended workloads.

Remove the lustre_lock and it's accessor functions l_lock(),
l_unlock(), l_lock_init(), and l_has_lock() since they have
not been used by the code since Lustre 1.6.

Lustre-Commit: 34b9fe2f703d91e7ad5b315aaac696d3a314cf0b
Lustre-Review: http://review.whamcloud.com/9294

Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: Iea30c0853faf1ff18821b1facd2020ef91df1764
Reviewed-on: http://review.whamcloud.com/12258
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>