staging/lustre: fix undefined reference if CONFIG_PROC_FS is off

When building Lustre with CONFIG_PROC_FS off, we'll get many errors like:

drivers/staging/lustre/lustre/obdclass/llog_test.c:1053: error: implicit declaration of function ‘lprocfs_llog_test_init_vars’
make[3]: *** [drivers/staging/lustre/lustre/obdclass/llog_test.o] Error 1
make[2]: *** [drivers/staging/lustre/lustre/obdclass] Error 2
make[2]: *** Waiting for unfinished jobs....
  CC [M]  drivers/staging/lustre/lustre/ptlrpc/ptlrpcd.o
drivers/staging/lustre/lustre/ptlrpc/pinger.c: In function ‘ptlrpc_pinger_main’:
drivers/staging/lustre/lustre/ptlrpc/pinger.c:331: error: implicit declaration of function ‘obd_update_maxusage’

The patch defines following symbols when CONFIG_PROC_FS is off:
fld_type_proc_dir, obd_update_maxusage(), obd_max_pages, obd_max_alloc, obd_alloc,
obd_pages, lprocfs_llog_test_init_vars().

Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>