Arduino.h: Add digitalPinToInterrupt

- Return the same number as long as not more than number of digital
  pins.
- This does not seem to be present in ArduinoCoreAPI but defined for all
  Arduino boards (and microblocks has started using it).
- Also present in arduino docs [1]

[1]: https://www.arduino.cc/reference/en/language/functions/external-interrupts/digitalpintointerrupt/

Signed-off-by: Ayush Singh <[email protected]>

Author: Ayush1325

Diff for: cores/arduino/Arduino.h

@@ -97,6 +97,10 @@ enum analogPins { DT_FOREACH_PROP_ELEM(DT_PATH(zephyr_user),
 
 #endif
 
+static inline int digitalPinToInterrupt(pin_size_t pin) {
+  return (pin < NUM_OF_DIGITAL_PINS) ? pin : -1;
+}
+
 void interrupts(void);
 void noInterrupts(void);