kunit: allow kunit to be loaded as a module

Making kunit itself buildable as a module allows for "always-on"
kunit configuration; specifying CONFIG_KUNIT=m means the module
is built but only used when loaded.  Kunit test modules will load
kunit.ko as an implicit dependency, so simply running
"modprobe my-kunit-tests" will load the tests along with the kunit
module and run them.
Co-developed-by: Knut Omang <knut.omang@oracle.com>
Signed-off-by: Knut Omang <knut.omang@oracle.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

lib/kunit/Kconfig

@@ -3,7 +3,7 @@
 #
 
 menuconfig KUNIT
-	bool "KUnit - Enable support for unit tests"
+	tristate "KUnit - Enable support for unit tests"
 	help
 	  Enables support for kernel unit tests (KUnit), a lightweight unit
 	  testing and mocking framework for the Linux kernel. These tests are

lib/kunit/Makefile

-obj-$(CONFIG_KUNIT) +=			test.o \
+obj-$(CONFIG_KUNIT) +=			kunit.o
+
+kunit-objs +=				test.o \
 					string-stream.o \
 					assert.o \
 					try-catch.o

lib/kunit/test.c

@@ -486,3 +486,16 @@ void kunit_cleanup(struct kunit *test)
 	}
 }
 EXPORT_SYMBOL_GPL(kunit_cleanup);
+
+static int __init kunit_init(void)
+{
+	return 0;
+}
+late_initcall(kunit_init);
+
+static void __exit kunit_exit(void)
+{
+}
+module_exit(kunit_exit);
+
+MODULE_LICENSE("GPL v2");