perf tools: Move u64_swap union

... to its single user's header, evsel.h.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/tip-9os1chjyz12upubfsjc71d99@git.kernel.org


Signed-off-by: Jiri Olsa <jolsa@kernel.org>