tests: drivers: counter: Add tests support for Renesas AGT timer

on mck_ra8t2 board

Add support for test app on Renesas mck_ra8t2:
- tests/drivers/counter/counter_basic_api

Signed-off-by: Khoa Tran <[email protected]>

Author: khoatranyj

tests/drivers/counter/counter_basic_api/boards/mck_ra8t2_r7ka8t2lfecac_cm85.overlay

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2025 Renesas Electronics Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&agt0 {
+	interrupts = <94 1>, <95 1>;
+	interrupt-names = "agti", "agtcmai";
+	renesas,count-source = "AGT_CLOCK_LOCO";
+	renesas,prescaler = <0>;
+	status = "okay";
+
+	counter0: counter {
+		status = "okay";
+	};
+};