perf trace: Allow associating scnprintf routines with well known arg names

perf trace: Allow associating scnprintf routines with well known arg names

For instance 'msr' appears in several tracepoints, so we can associate
it with a single scnprintf() routine auto-generated from kernel headers,
as will be done in followup patches.

Start with an empty array of associations.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-89ptht6s5fez82lykuwq1eyb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>