staging: ramster: Provide accessory functions for counter decrease

This patch enables these functions to be wrapped and
can disable/enable this with CONFIG_DEBUG_FS.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>