kpatch-patch-hook: fix incorrect old_offsets for loadable modules

Fix incorrect old_offsets for loadable modules during sysfs
initialization in patch_init by dynamically resolving the old addresses
of module functions at module load time.

If the module is already loaded, resolve the function address using
kpatch_find_module_symbol(), as the old_offset supplied in .kpatch.funcs
is unusable since the address of a function from a module cannot be
known until runtime.

If the module has not been loaded at the time the patch module is loaded,
have kpatch_module_notify call a sysfs hook (kpmod.add_func_sysfs)
that will populate the sysfs directory once the module loads.