The perf_time_to_tsc and tsc_to_perf_time functions are only used for x86.

Make inclusion of tsc.c dependent on x86 as well.
Signed-off-by: David Ahern <david.ahern@oracle.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <david.ahern@oracle.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1424370153-128274-1-git-send-email-david.ahern@oracle.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>