LU-8066 sysfs: migrate max_pages_per_rpc to sysfs tree

LU-8066 sysfs: migrate max_pages_per_rpc to sysfs tree

Both the osc and mdc layer place max_pages_per_rpc in the proc
tree. We can move it to the sysfs tree. This is a simple sysfs
file so no root only issues for this tunable.

Change-Id: Ib4c9bd5e3b6a56c489149779208a1461692538ac
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56665
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>