nrf: Update main.c to init relevant board drivers, if enabled.

If the board has these drivers then they will be initialized:
- softpwm (implicit ticker)
- music module
- board specific module

ports/nrf/main.c

@@ -61,6 +61,11 @@
 #include "ble_uart.h"
 #endif
 
+#if MICROPY_PY_MACHINE_SOFT_PWM
+#include "ticker.h"
+#include "softpwm.h"
+#endif
+
 void do_str(const char *src, mp_parse_input_kind_t input_kind) {
     mp_lexer_t *lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
     if (lex == NULL) {
@@ -206,6 +211,23 @@ pin_init0();
     }
 #endif
 
+#if MICROPY_PY_MACHINE_SOFT_PWM
+    ticker_init0();
+    softpwm_init0();
+#endif
+
+#if MICROPY_PY_MUSIC
+    microbit_music_init0();
+#endif
+#if BOARD_SPECIFIC_MODULES
+    board_modules_init0();
+#endif
+
+#if MICROPY_PY_MACHINE_SOFT_PWM
+    ticker_start();
+    pwm_start();
+#endif
+
     for (;;) {
         if (pyexec_mode_kind == PYEXEC_MODE_RAW_REPL) {
             if (pyexec_raw_repl() != 0) {