tests: dma: siwx917_rb4342a: Add chan_blen_transfer overlay files

This commit adds the DMA overlay and config file for the brd4342a board,
enabling chan_blen_transfer support in Zephyr.

Upstream-status: available
Signed-off-by: S Mohamed Fiaz <[email protected]>
(cherry picked from commit 08b55fa)

Author: fimohame

tests/drivers/dma/chan_blen_transfer/boards/siwx917_rb4342a.conf

@@ -0,0 +1,2 @@
+CONFIG_DMA_TRANSFER_CHANNEL_NR_0=0
+CONFIG_DMA_TRANSFER_CHANNEL_NR_1=7

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

@@ -0,0 +1,11 @@
+/*
+ * Copyright (c) 2025 Silicon Laboratories, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&gpdma {
+	status = "okay";
+};
+
+tst_dma0: &gpdma {};