LU-1282 lprocfs: Add a module param to disable percpu stats

LU-1282 lprocfs: Add a module param to disable percpu stats

Add an obdclass module option to choose to use a single lprocfs stats
structure rather than percpu data.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I45d5a05029197e629d4f7d161a5e4e5d01a93bf5
Reviewed-on: http://review.whamcloud.com/2515
Tested-by: Hudson
Reviewed-by: Christopher J. Morrone <chris.morrone.llnl@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>