export funcs via sysfs

This feature is implemented as:
```
# insmod ./kpatch-meminfo.ko
# ls /sys/kernel/kpatch/patches/kpatch_meminfo/functions/meminfo_proc_show/
new_addr  old_addr
# cat /sys/kernel/kpatch/patches/kpatch_meminfo/functions/meminfo_proc_show/new_addr 
0xffffffffa05211e0
# cat /sys/kernel/kpatch/patches/kpatch_meminfo/functions/meminfo_proc_show/old_addr 
0xffffffff8125d0e0
```