selftests/mm: mlock2-tests: conform test to TAP format output

Conform the layout, informational and status messages to TAP.  No
functional change is intended other than the layout of output messages. 
I've done some cleanups as well.

Link: https://lkml.kernel.org/r/20240202113119.2047740-6-usama.anjum@collabora.comSigned-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/mlock2.h

@@ -6,12 +6,7 @@
 
 static int mlock2_(void *start, size_t len, int flags)
 {
-#ifdef __NR_mlock2
 	return syscall(__NR_mlock2, start, len, flags);
-#else
-	errno = ENOSYS;
-	return -1;
-#endif
 }
 
 static FILE *seek_to_smaps_entry(unsigned long addr)
@@ -27,10 +22,8 @@ static FILE *seek_to_smaps_entry(unsigned long addr)
 	char path[BUFSIZ];
 
 	file = fopen("/proc/self/smaps", "r");
-	if (!file) {
-		perror("fopen smaps");
-		_exit(1);
-	}
+	if (!file)
+		ksft_exit_fail_msg("fopen smaps: %s\n", strerror(errno));
 
 	while (getline(&line, &size, file) > 0) {
 		if (sscanf(line, "%lx-%lx %s %lx %s %lu %s\n",