Change nRF RTC implementation to use RTC2 micropython#1046

(to avoid interference with Bluetooth Softdevice. See
adafruit#1534 (comment)
with thanks to @bboser for pointing it out)

Author: nickzoic

ports/nrf/common-hal/rtc/RTC.c

@@ -43,7 +43,7 @@
 
 volatile static uint32_t rtc_offset = 0;
 
-const nrfx_rtc_t rtc_instance = NRFX_RTC_INSTANCE(0);
+const nrfx_rtc_t rtc_instance = NRFX_RTC_INSTANCE(2);
 
 const nrfx_rtc_config_t rtc_config = {
 	.prescaler = RTC_FREQ_TO_PRESCALER(RTC_CLOCK_HZ),

ports/nrf/nrfx_config.h

@@ -72,6 +72,8 @@
 
 #define NRFX_RTC_ENABLED 1
 #define NRFX_RTC0_ENABLED 1
+#define NRFX_RTC1_ENABLED 1
+#define NRFX_RTC2_ENABLED 1
 
 // TIMERS
 #define NRFX_TIMER_ENABLED 1