Use analogPinToChannel() macro if present for ATtiny25/45/85.

This allows use of A0, A1, A2, A3 constants and for them to be mapped to the appropriate analog input channel. It should only be used if the macro is actually defined.

(Filtered from arduino/Arduino@ebc3501)

Author: damellis

core/wiring_analog.c

@@ -47,6 +47,8 @@ int analogRead(uint8_t pin)
 	if (pin >= 18) pin -= 18; // allow for channel or pin numbers
 #elif defined(__AVR_ATmega1284P__) || defined(__AVR_ATmega644P__)
 	if (pin >= 24) pin -= 24; // allow for channel or pin numbers
+#elif defined(analogPinToChannel) && (defined(__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__))
+	pin = analogPinToChannel(pin);
 #else
 	if (pin >= 14) pin -= 14; // allow for channel or pin numbers
 #endif