perf tools: Add union u64_swap type for swapping u64 data

The following union:
  union {
        u64 val64;
        u32 val32[2];
  } u;

is used on more than one place in perf code and will be used more in
upcomming patches.

Adding union u64_swap to have it defined globaly so we dont need to
redefine it all the time.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1337151548-2396-4-git-send-email-jolsa@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>