LU-13258 llite: bind readahead workqueue to CPT set

LU-13258 llite: bind readahead workqueue to CPT set

A workqueue is used by Lustre to optimize readahead. This work
queue can run on any core and can easily be over surscribed. This
will have a negative impact on HPC applications running on a
Lustre client. Limit the number of threads a workqueue can run
to the size of the CPU allocated for Lustre and only allow those
threads to run on the cores belonging to the CPT set.

Change-Id: Ifcc662d52843f5028c34d55695c1d6297e5c00b0
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/37717
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Stephen Champion <stephen.champion@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>