test: Rename unit-test flags

The UT_TESTF_ macros read as 'unit test test flags' which is not right.
Rename to UTF ('unit test flags').

This has the benefit of being shorter, which helps keep UNIT_TEST()
declarations on a single line.

Give the enum a name and reference it from the UNIT_TEST() macros while
we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/virtio.c b/test/dm/virtio.c
index 3efd7c7..2574c4d 100644
--- a/test/dm/virtio.c
+++ b/test/dm/virtio.c
@@ -29,4 +29,4 @@
 
 	return 0;
 }
-DM_TEST(dm_test_virtio_missing_ops, UT_TESTF_SCAN_PDATA | UT_TESTF_SCAN_FDT);
+DM_TEST(dm_test_virtio_missing_ops, UTF_SCAN_PDATA | UTF_SCAN_FDT);