* remove "cpu features" that are actually just processors
* rename `v8` to `v8a`. this matches the corresponding
change to target/aarch64.zig
* rename types in preparation for removing sub-architecture
from `std.Target`.
I have other files changed in my dirty working tree, but about to make
some changes to arm.zig that I don't want batched with this commit.
4c6f207aff