LU-3059 dt: shrink dt_object by 8 bytes on x86_64

LU-3059 dt: shrink dt_object by 8 bytes on x86_64

Merge struct dt_lock_operations (containing only do_object_lock) into
dt_object_operations.  The DT types that use these two structures do
not have enough variation in their methods to justify separate
structures and it removes an 8 byte pointer member from struct
dt_object.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I4372ba23f0f7691ac86e391772a6a6157311cfda
Reviewed-on: http://review.whamcloud.com/5892
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>