staging/lustre/ldlm: Add infrastructure to move ldlm pool controls to sysfs

This adds registration of /sys/fs/lustre/ldlm/namespaces/.../pool
dir.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>