kallsyms: Make kallsyms_on_each_symbol generally available

Making kallsyms_on_each_symbol generally available, so it can be
used outside CONFIG_LIVEPATCH option in following changes.

Rather than adding another ifdef option let's make the function
generally available (when CONFIG_KALLSYMS option is defined).

Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220510122616.2652285-2-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>