This patch introduce one sysfs attribute of "using" to klp_func. For example, if there are serval patches make changes to function "meminfo_proc_show", the attribute "enabled" of all the patch is 1. With this attribute, we can easily know the version enabling belongs to which patch. Changes v1 => v2: 1. reset using type from bool to int 2. the value of "using" contains 3 types, 0(not used), 1(using), -1(unknown). (As suggested by Petr). 3. add the process of transition state (-1 state). (suggested by Petr and Miroslav) v1: https://lore.kernel.org/live-patching/1A0E6D0A-4245-4F44-8667-CDD86A925347@xxxxxxxxx/T/#t
