LU-8066 llite: move /proc/fs/lustre/llite/xattr_cache to sysfs

LU-8066 llite: move /proc/fs/lustre/llite/xattr_cache to sysfs

Move xattr_cache file from /proc/fs/lustre/llite/*
to /sys/fs/lustre/llite/*/

This is a modified version of

Linux-commit: 070c29ca79ef5a3ba753053928371b257064b15f

Change-Id: I0fa7715cd2ae9c90af1540e406c1645a8eee3b2e
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/32507
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>