Change digitalPinToInterrupt to return pin, and use g_APinDescription[pin].ulExtInt to map pin inside attachInterrupt/detachInterrupt

This brings things inline with the atachInterrupt documentation for
usage:
attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);

Author: sandeepmistry

cores/arduino/WInterrupts.c

@@ -57,7 +57,7 @@ void attachInterrupt(uint32_t pin, voidFuncPtr callback, uint32_t mode)
   uint32_t config;
   uint32_t pos;
 
-  EExt_Interrupts in = digitalPinToInterrupt(pin);
+  EExt_Interrupts in = g_APinDescription[pin].ulExtInt;
   if (in == NOT_AN_INTERRUPT || in == EXTERNAL_INT_NMI)
     return;
 
@@ -116,7 +116,7 @@ void attachInterrupt(uint32_t pin, voidFuncPtr callback, uint32_t mode)
  */
 void detachInterrupt(uint32_t pin)
 {
-  EExt_Interrupts in = digitalPinToInterrupt(pin);
+  EExt_Interrupts in = g_APinDescription[pin].ulExtInt;
   if (in == NOT_AN_INTERRUPT || in == EXTERNAL_INT_NMI)
     return;
 

variants/arduino_zero/variant.h

@@ -77,7 +77,7 @@ extern "C"
 // #define digitalPinToTimer(P)
 
 // Interrupts
-#define digitalPinToInterrupt(P)   ( g_APinDescription[P].ulExtInt )
+#define digitalPinToInterrupt(P)   ( P )
 
 // LEDs
 #define PIN_LED_13           (13u)