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/nop.c b/test/dm/nop.c
index 0c79431..7eac167 100644
--- a/test/dm/nop.c
+++ b/test/dm/nop.c
@@ -70,4 +70,4 @@
 	return 0;
 }
 
-DM_TEST(dm_test_nop, UT_TESTF_FLAT_TREE | UT_TESTF_SCAN_FDT);
+DM_TEST(dm_test_nop, UTF_FLAT_TREE | UTF_SCAN_FDT);