LU-1756 kernel: cleanup lustre_compat25.h

Use cpumask_of_node() rather than node_to_cpumask().
cpumask_of_node() is availabe in latest kernel, while
node_to_cpumask() isn't.

Also fix how cpumask_of_node() is detected. Some OFED
backports cpumask_of_node() and put it in private
include/linux/cpumask.h.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: I770fcb549c354c2c925c821d2a8920d867274d7a
Reviewed-on: http://review.whamcloud.com/4588
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>