arm64: start defining a std.apple configuration

[kevans]

Summary

The M1 has an IOMMU, FDT, and bge to start with. Add a SOC_* option for
the first SoC we'll be supporting.

[• karels]

Looks good to me too.

[jrtc27]

sys/arm64/conf/std.apple

8

Doesn't this have the side-effect of enabling IOMMU use for every other platform GENERIC runs on? That code isn't well-tested on arm64.

[jrtc27]

sys/arm64/conf/std.apple

8

For example, https://github.com/CTSRD-CHERI/cheribsd/pull/1571/commits/f6e9a195422f949585ab40cb8515afab1179b83e is an issue we've found (not yet committed since we still aren't enabling IOMMU use downstream either)

[kevans]

sys/arm64/conf/std.apple

8

I'll remove it pre-commit; the actual IOMMU bits of my DART driver aren't 100% functional anyways, so I'll likely upstream a version of that without the IOMMU integration (i.e. any DART that supports bypass mode will be configured as such so that we at least get some usb ports and stuff with GENERIC)