tests: drivers: counter: Add counter_basic_api overlay file

This commit adds the counter_basic_api overlay file for the
brd4338a board,enabling counter support.

Upstream-status: available
Signed-off-by: S Mohamed Fiaz <[email protected]>
(cherry picked from commit 8c5e3d0)

Author: fimohame

tests/drivers/counter/counter_basic_api/boards/siwx917_rb4338a.overlay

@@ -0,0 +1,8 @@
+/*
+ * Copyright (c) 2025 Silicon Laboratories Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+&sysrtc0 {
+	status = "okay";
+};