VAES intrinsics are unsafe, but shouldn't be

[nazar-pc]

Currently VAES intrinsics like _mm512_aesenc_epi128 are unsafe, while regular AES-NI intrinsics like _mm_aesenc_si128 are safe.

I have not found an explanation for this, so I assume they shouldn't be unsafe.

rust-lang/rust#111137 doesn't seem to contain any details about what stabilization of them would look like, but hopefully they'll be stabilized in a safe form.

[aDotInTheVoid]

Transferring to stdarch, as that's where the intrinsic are defined.

CC #1714

@rustbot transfer stdarch