[arduino] add F_CPU to indicate the frequency of CPU

bsp/stm32/stm32f072-st-nucleo/applications/arduino_pinout/pins_arduino.h

@@ -38,6 +38,7 @@
 #define A6   (23)
 #define A7   (24)
 
+#define F_CPU  48000000L /* CPU: 48MHz */
 #define LED_BUILTIN  D13 /* Default Built-in LED */
 
 #define RTDUINO_DEFAULT_IIC_BUS_NAME            "i2c1"

bsp/stm32/stm32f401-st-nucleo/applications/arduino_pinout/pins_arduino.h

@@ -38,6 +38,7 @@
 #define A6   (23)
 #define A7   (24)
 
+#define F_CPU  84000000L /* CPU: 84MHz */
 #define LED_BUILTIN  D13 /* Default Built-in LED */
 
 #define RTDUINO_DEFAULT_IIC_BUS_NAME            "i2c1"

bsp/stm32/stm32l475-atk-pandora/applications/arduino_pinout/pins_arduino.h

@@ -44,6 +44,7 @@
 #define A3   (29)
 #define DAC0 (30)
 
+#define F_CPU  80000000L /* CPU: 80MHz */
 #define LED_BUILTIN  D22 /* Default Built-in LED */
 
 /*