selftests/powerpc: Give some tests longer to run

Some of these long running tests can time out on heavily loaded
systems, give them longer to run.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/benchmarks/mmap_bench.c

@@ -84,5 +84,7 @@ int main(int argc, char *argv[])
 			exit(1);
 		}
 	}
+
+	test_harness_set_timeout(300);
 	return test_harness(test_mmap, "mmap_bench");
 }