tests: drivers: counter_brf_rtc: test fixed top on nRF52832

Added overlay for the board.

Signed-off-by: Michał Stasiak <michal.stasiak@nordicsemi.no>

Author: mstasiaknordic

tests/drivers/counter/counter_nrf_rtc/fixed_top/boards/nrf52dk_nrf52832.overlay

@@ -0,0 +1,8 @@
+&rtc0 {
+	status = "okay";
+	fixed-top;
+};
+&rtc2 {
+	status = "okay";
+	fixed-top;
+};