staging/lustre/lu: shrink lu_object by 8 bytes on x86_64

Remove the lo_depth member from struct lu_object.  This field is never
set and only read in lu_object_print().  Remove the lo_flags member.
This field was only used in lu_object_alloc() and can be replaced with
an on-stack mask to keep trace of which layers have been allocated.

Lustre-change: http://review.whamcloud.com/5890
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3059


Signed-off-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>