perf trace: Mark the 'head' arg in the set_robust_list syscall as coming from user space

With that it uses the generic BTF based pretty printer:

This one we need to think about, not being acquainted with this syscall,
should we _traverse_ that list somehow? Would that be useful?

  root@number:~# perf trace -e set_robust_list sleep 1
       0.000 ( 0.004 ms): sleep/1206493 set_robust_list(head: (struct robust_list_head){.list = (struct robust_list){.next = (struct robust_list *)0x7f48a9a02a20,},.futex_offset = (long int)-32,}, len: 24) =
  root@number:~#

strace prints the default integer args:

  root@number:~# strace -e set_robust_list sleep 1
  set_robust_list(0x7efd99559a20, 24)     = 0
  +++ exited with 0 +++
  root@number:~#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org
Link: https://lore.kernel.org/lkml/ZuH6MquMraBvODRp@x1


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