kunit: move string-stream.h to lib/kunit

string-stream interfaces are not intended for external use;
move them from include/kunit to lib/kunit accordingly.

Co-developed-by: Knut Omang <[e-mail]>
Signed-off-by: Knut Omang <[e-mail]>
Signed-off-by: Alan Maguire <[e-mail]>
Reviewed-by: Brendan Higgins <[e-mail]>
Tested-by: Brendan Higgins <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

include/kunit/assert.h

···
 #ifndef _KUNIT_ASSERT_H
 #define _KUNIT_ASSERT_H
 
-#include <kunit/string-stream.h>
 #include <linux/err.h>
+#include <linux/kernel.h>
 
 struct kunit;
+struct string_stream;
 
 /**
  * enum kunit_assert_type - Type of expectation/assertion.

lib/kunit/assert.c

···
  */
 #include <kunit/assert.h>
 
+#include "string-stream.h"
+
 void kunit_base_assert_format(const struct kunit_assert *assert,
 			      struct string_stream *stream)
 {

lib/kunit/string-stream-test.c

···
  * Author: Brendan Higgins <[e-mail]>
  */
 
-#include <kunit/string-stream.h>
 #include <kunit/test.h>
 #include <linux/slab.h>
+
+#include "string-stream.h"
 
 static void string_stream_test_empty_on_creation(struct kunit *test)
 {

lib/kunit/string-stream.c

···
  * Author: Brendan Higgins <[e-mail]>
  */
 
-#include <kunit/string-stream.h>
 #include <kunit/test.h>
 #include <linux/list.h>
 #include <linux/slab.h>
+
+#include "string-stream.h"
 
 struct string_stream_fragment_alloc_context {
 	struct kunit *test;

lib/kunit/test.c

···
 #include <linux/kernel.h>
 #include <linux/sched/debug.h>
 
+#include "string-stream.h"
+
 static void kunit_set_failure(struct kunit *test)
 {
 	WRITE_ONCE(test->success, false);