objtool: Print top level commands on incorrect usage

Print top-level objtool commands, along with the error on incorrect
command line usage. Objtool command line parser exit's with code 129,
for incorrect usage. Convert the cmd_usage() exit code also, to maintain
consistency across objtool.

After the patch:

  $ ./objtool -j

  Unknown option: -j

  usage: objtool COMMAND [ARGS]

  Commands:
     check   Perform stack metadata validation on an object file
     orc     Generate in-place ORC unwind tables for an object file

  $ echo $?
  129
Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1507992474-16142-1-git-send-email-kamalesh@linux.vnet.ibm.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

tools/objtool/objtool.c

@@ -70,7 +70,7 @@ static void cmd_usage(void)
 
 	printf("\n");
 
-	exit(1);
+	exit(129);
 }
 
 static void handle_options(int *argc, const char ***argv)
@@ -86,9 +86,7 @@ static void handle_options(int *argc, const char ***argv)
 			break;
 		} else {
 			fprintf(stderr, "Unknown option: %s\n", cmd);
-			fprintf(stderr, "\n Usage: %s\n",
-				objtool_usage_string);
-			exit(1);
+			cmd_usage();
 		}
 
 		(*argv)++;