nrf/nrfx_config: Disable RTC2 for nRF9160 targets.

nRF9160 does not have any RTC2. Disable the configuration in
case of NRF9160_XXAA.

ports/nrf/nrfx_config.h

@@ -130,7 +130,7 @@
 #define NRFX_RTC_ENABLED (MICROPY_PY_MACHINE_RTCOUNTER)
 #define NRFX_RTC0_ENABLED 1
 #define NRFX_RTC1_ENABLED 1
-#define NRFX_RTC2_ENABLED (!NRF51)
+#define NRFX_RTC2_ENABLED (!NRF51) && (!NRF9160_XXAA)
 
 #define NRFX_TIMER_ENABLED (MICROPY_PY_MACHINE_TIMER)
 #define NRFX_TIMER0_ENABLED 1