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/Kconfig b/test/Kconfig
index 3270c84..6f918ed 100644
--- a/test/Kconfig
+++ b/test/Kconfig
@@ -1,3 +1,6 @@
+config UNIT_TEST
+	bool
+
 config CMD_UT_TIME
 	bool "Unit tests for time functions"
 	help