LU-12820 osc: remove 'transient' arg from osc_enter_cache_try

LU-12820 osc: remove 'transient' arg from osc_enter_cache_try

This arg is always '0', so remove it.
Consequently, OBD_BRW_NOCACHE is never set, and
cl_dirty_transit and obd_dirty_transit_pages
are never non-zero, so they can be removed as well.

Lustre-change: https://review.whamcloud.com/36319
Lustre-commit: 524deb6f985beb512a4499501fd7275ecb77f815

Patch also includes changes for atomic ops optimization
to keep in sync with master branch:

Lustre-change: https://review.whamcloud.com/33859
Lustre-commit: 8b364fbd6bd9e0088440e6d6837861a641b923a0

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: Ia047affc33fb9277e6c28a8f6d7d088c385b51a8
Reviewed-on: https://review.whamcloud.com/39518
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>