selftests/vm: skip 128TBswitch on unsupported arch

The test va_128TBswitch.c exercises a feature only supported on PPC and
x86_64, but it's run on other 64-bit archs as well. Before this patch,
the test did nothing and returned 0 for KSFT_PASS. This patch makes it
return the KSFT codes from kselftest.h, including KSFT_SKIP when
appropriate.

Verified on arm64 and x86_64.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Adam Sindelar <[e-mail]>
Cc: David Vernet <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/vm/va_128TBswitch.c

···
 static int run_test(struct testcase *test, int count)
 {
 	void *p;
-	int i, ret = 0;
+	int i, ret = KSFT_PASS;
 
 	for (i = 0; i < count; i++) {
 		struct testcase *t = test + i;
···
 
 		if (p == MAP_FAILED) {
 			printf("FAILED\n");
-			ret = 1;
+			ret = KSFT_FAIL;
 			continue;
 		}
 
 		if (t->low_addr_required && p >= (void *)(ADDR_SWITCH_HINT)) {
 			printf("FAILED\n");
-			ret = 1;
+			ret = KSFT_FAIL;
 		} else {
 			/*
 			 * Do a dereference of the address returned so that we catch
···
 	int ret;
 
 	if (!supported_arch())
-		return 0;
+		return KSFT_SKIP;
 
 	ret = run_test(testcases, ARRAY_SIZE(testcases));
 	if (argc == 2 && !strcmp(argv[1], "--run-hugetlb"))