Incomplete pin definitions for Sparkfun SAMD51 Thing PLus

[ajahern95]

The pin definitions does not fully line up with the pinout of the SAMD51 Thing Plus pin out, as seen here: https://cdn.sparkfun.com/assets/c/a/8/6/8/ThingPlusSamD51a.pdf

For example, D9 the interrupt and analog is not attached, nor analog on D4. D9 is important on the Adafruit Music Maker Feather Shield (https://www.adafruit.com/product/3436), as it is used as an interrupt to allow background music playback. In the current state, background music playing results in nothing happening. For a new or unexperienced user, they might think that either the Thing Plus or Music Maker shield is broken.

Original line for D9 in variants.cpp: { PORTA, 7, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }

Possible corrections: { PORTA, 7, PIO_DIGITAL, PIN_ATTR_DIGITAL, ADC_Channel7, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_7 }.