staging/lustre/ptlrpc: move sptlrpc procfs entry to debugfs

We might want eventuall split it into a bunch of
single-value sysfs entries, I imagine, but there is no urgent need now.

Signed-off-by: Dmitry Eremin <dmiter4ever@gmail.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>