Feature/68000 probe support

[roscopeco]

Happy to discuss this one, it's kind of a big change (conceptually, if not actually from the code POV).

• Support device probing on 68000 CPUs (with a bit of stack hackery in the bus error handler)
• Switch default CPU for Firmware build to be "lowest comment denominator" 68000
• Switch default CPU for software to 68000 for the same reasons
• Fail fast (and polite) in memcheck on 68000

Additionally, this:

• Prepares ATA / IDE for (possible) future deprecation / removal from standard build

This just means I made a new make option WITH_ATA - I needed this bit while developing, and it seemed like it could be useful down the line so left it in. It's on by default (so no change).

I have tested this on 68000, 68010 and it seems fine. ~If anyone has a populated 020 handy it would be good to double check it hasn't broken anything there~ Edit: This has now been successfully tested on 020 as well.

Proof of life, no rebuild between these runs - just yanking and moving the chips:

[roscopeco]

As far as I can tell, it looks good! I've only got a 68010 running, so I can't confirm the other CPUs, but what's there makes sense. 👍

Thanks for the review @0xTJ 🙌

For the sake of posterity I put a screenshot in the description with proof it boots to Kermit on the bottom three 68k models 🙂