tests: dma: siwx91x: loop_transfer test support

Add siwx917_rb4338a and siwx917_rb4342a overlays
for loop_transfer test

Signed-off-by: Sai Santhosh Malae <Santhosh.Malae@silabs.com>

Author: smalae

tests/drivers/dma/loop_transfer/boards/siwx917_rb4338a.overlay

@@ -0,0 +1,10 @@
+/*
+ * Copyright (c) 2025 Silicon Laboratories Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+&dma0 {
+	status = "okay";
+};
+
+tst_dma0: &dma0 { };

tests/drivers/dma/loop_transfer/boards/siwx917_rb4342a.overlay

@@ -0,0 +1,10 @@
+/*
+ * Copyright (c) 2025 Silicon Laboratories Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+&dma0 {
+	status = "okay";
+};
+
+tst_dma0: &dma0 { };