perf parse-regs: Improve error output when faced with unknown register name

Add quotes around the register name and suggest using 'perf record -I?'
to get the list of available registers.

Before:

  # perf record -Idi,xmm20,xmm1
  Warning:
  unknown register xmm20, check man page

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

      -I, --intr-regs[=<any register>]
                            sample selected machine registers on interrupt, use -I ? to list register names
  #
  # perf record -Idi,xmm20,xmm1
  Warning:
  unknown register "xmm20", check man page or run "perf record -I?"

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

      -I, --intr-regs[=<any register>]
                            sample selected machine registers on interrupt, use -I ? to list register names
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lkml.kernel.org/n/tip-9a9hyuum8c0oggg86xd3sxc5@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-regs-options.c

@@ -48,8 +48,7 @@ parse_regs(const struct option *opt, const char *str, int unset)
 					break;
 			}
 			if (!r->name) {
-				ui__warning("unknown register %s,"
-					    " check man page\n", s);
+				ui__warning("Unknown register \"%s\", check man page or run \"perf record -I?\"\n", s);
 				goto error;
 			}