boards/arduino-atmega-common: use PD7 for ctx operations

This was previously configured to PC5 which is shared with the i2c
SCL line. PD7 is selected since it's the only pin which does not
have an additional function.

boards/arduino-atmega-common/include/board_common.h

@@ -65,12 +65,12 @@ extern "C" {
  */
 #ifdef CPU_ATMEGA328P
 #define AVR_CONTEXT_SWAP_INIT do { \
-            DDRC |= (1 << PC5); \
-            PCICR |= (1 << PCIE1); \
-            PCMSK1 |= (1 << PCINT13); \
+            DDRD |= (1 << PD7); \
+            PCICR |= (1 << PCIE2); \
+            PCMSK2 |= (1 << PCINT23); \
 } while (0)
-#define AVR_CONTEXT_SWAP_INTERRUPT_VECT  PCINT1_vect
-#define AVR_CONTEXT_SWAP_TRIGGER   PORTC ^= (1 << PC5)
+#define AVR_CONTEXT_SWAP_INTERRUPT_VECT  PCINT2_vect
+#define AVR_CONTEXT_SWAP_TRIGGER   PORTD ^= (1 << PD7)
 #endif
 
 #ifdef CPU_ATMEGA2560