LU-6245 libcfs: use libcfs_private.h only for kernel space

The current lustre userland code no longer uses special
macros which are present in libcfs_private.h.
We can then eliminate those macros and only use the
libcfs_private.h header for kernel space. The special
macros no longer needed for userland are:

1) LOGL and LOGU which were used in the UAPI header
   lustre_cfg.h and lustre_ioctl.h.

2) [un]likely macros used in the UAPI header lustre_ostid.h

3) The special libcfs assert macros

Change-Id: Iaa54bdcfb6104d13f2aabae63335e041481244a5
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/22138
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>