perf trace: Separate 'struct syscall_fmt' definition from syscall_fmts variable

perf trace: Separate 'struct syscall_fmt' definition from syscall_fmts variable

As this has all the things needed to format tracepoints events, not just
syscalls, that, after all, are just tracepoints with a set in stone ABI,
i.e. order and number of parameters.

For tracepoints we'll create a

  static struct syscall_fmt tracepoint_fmts[]

array and will fill the ->arg[] entries with the beautifier for each
positional argument and record the name, then, when we need it, we'll
just check that the position has the same name, maybe even type, so that
we can do some check that the tracepoint hasn't changed, if it has, we
can even reorder things.

Keep calling it syscall_fmt but use it as well for tracepoints, do it
this way to minimize changes and reuse what is in place for syscalls,
we'll see.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-2x1jgiev13zt4njaanlnne0d@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>