Add platform independent delay abstraction

Makefile

@@ -33,6 +33,7 @@ OPT = 3
 C_FLAGS += -O$(OPT) -g$(OPT)
 C_FLAGS += -Wall -Werror
 C_FLAGS += -ffunction-sections -fdata-sections -fno-strict-aliasing
+C_FLAGS += -DPLATFORM_$(PLATFORM)
 
 LIBS += c nosys m
 

include/delay.h

@@ -0,0 +1,10 @@
+#ifndef __DELAY_H__
+#define __DELAY_H__
+
+#if defined(PLATFORM_nrf52)
+    #include "nrf_delay.h"
+
+    #define delay_ms    nrf_delay_ms
+#endif
+
+#endif