sam: add support for pin change interrupts (samd5x)

[sago35]

#1094
#1111

I wrote the code for SAMD51J19A and SAMD51J20A.
I checked with feather-m4 and pyportal, and it seems to be working fine.

https://github.com/sago35/tinygo/tree/interrupts-pins-samd51

I'm struggling with how to write the following parts.
Is there a better way to do it?

1. sam.EIC.CTRLA.Set(0) or sam.EIC.CTRLA.ClearBits(0x02)
   • https://github.com/sago35/tinygo/blob/interrupts-pins-samd51/src/machine/machine_atsamd51.go#L352
2. Is it better to define it outside of SetInterrupt()?
   • https://github.com/sago35/tinygo/blob/interrupts-pins-samd51/src/machine/machine_atsamd51.go#L384
3. I'd like to write a little nicer, but interrupt.New() only accepts const values, so this is how it's implemented.
   • https://github.com/sago35/tinygo/blob/interrupts-pins-samd51/src/machine/machine_atsamd51.go#L393
4. I want to make an example, but the feather-m4 I have doesn't have a button.
   Creating an example for pybadge is one thing, but since there is no machine.Button, the other examples need to be modified.
   • Since wioterminal has a button, I'm going to make examples with Seeed WioTerminal support #1124.

[sago35]

The SAMD51P19 has 128 pins, so there's a bit more code.
Also, since the 128 pin setting is not yet in machine_atsamd51.go, it would be better to change it in #1124.

[sago35]

@deadprogram
I cherry-picked it.

[deadprogram]

Now merging, thanks for working on this @sago35

[deadprogram]

You might want to submit another PR to change sam.EIC.CTRLA.ClearBits(0x02) to sam.EIC.CTRLA.ClearBits(sam.EIC_CTRLA_ENABLE)