ARM64: add thunderbolt to `std.apple`

[ngie]

Summary

Apple has supported thunderbolt in all of the Apple Silicon consumer
devices that run macOS [1], e.g., the MacBook Air, MacBook Pro, etc.

Enable the thunderbolt driver in std.apple to help support this
hardware feature.

MFC after: 1 month

References:

1. https://support.apple.com/en-us/109523

[andrew]

Where is the thunderbolt device defined? I don't see it in main.

[ngie]

In D55556#1271225, @andrew wrote:

Where is the thunderbolt device defined? I don't see it in main.

Good call out. This is a bit cart-before-the-horse as it depends on other changes to make thunderbolt build with KERNCONF/some !THUNDERBOLT_DEBUG fixes.
I'll be posting a diff soon.