arm64: update instruction set attribute register definitions

This adds definitions for the latest additions to the AA64ISAR[01] ID
registers. This brings these registers in sync with ARMv8.6 initial spec
release.

An future change will parse many of these fields for HWCAP features.

Reviewed by: andrew, manu, markj (all previous versions)
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D26029