test: Move the unit tests to their own menu

Make all unit tests selectable as a menu of test suites instead of just
sitting in the top-level menu individually.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Kconfig b/test/dm/Kconfig
index 0fa3074..e5b341e 100644
--- a/test/dm/Kconfig
+++ b/test/dm/Kconfig
@@ -1,7 +1,6 @@
 config UT_DM
 	bool "Enable driver model unit test command"
-	depends on SANDBOX
-	select UNIT_TEST
+	depends on SANDBOX && UNIT_TEST
 	help
 	  This enables the 'ut dm' command which runs a series of unit
 	  tests on the driver model code. Each subsystem (uclass) is tested.