nrf: Enable -g flag by default.

This does not affect binary output, but makes debugging a whole lot
easier.

ports/nrf/Makefile

@@ -93,7 +93,7 @@ endif
 
 
 CFLAGS += $(CFLAGS_MCU_$(MCU_SERIES)) 
-CFLAGS += $(INC) -Wall -Werror -ansi -std=gnu99 -nostdlib $(COPT) $(NRF_DEFINES) $(CFLAGS_MOD)
+CFLAGS += $(INC) -Wall -Werror -g -ansi -std=gnu99 -nostdlib $(COPT) $(NRF_DEFINES) $(CFLAGS_MOD)
 CFLAGS += -fno-strict-aliasing
 CFLAGS += -fstack-usage
 CFLAGS += -Iboards/$(BOARD)