test: Generalize the unit test framework

Separate the ability to define tests and assert status of test functions
from the dm tests so they can be used more consistently throughout all
tests.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Kconfig b/test/dm/Kconfig
index a9d0298..3ca154f 100644
--- a/test/dm/Kconfig
+++ b/test/dm/Kconfig
@@ -1,6 +1,7 @@
 config DM_TEST
 	bool "Enable driver model test command"
 	depends on SANDBOX && CMD_DM
+	select UNIT_TEST
 	help
 	  This enables the 'dm test' command which runs a series of unit
 	  tests on the driver model code. Each subsystem (uclass) is tested.