Define auxtrace record alignment so that it can be referenced elsewhere.

Note this is preparation for patch "perf intel-pt: Fix overlap calculation
for padding"
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20190206103947.15750-2-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>