arm64: update instruction set attribute register definitions
This adds definitions for the latest additions to the AA64ISAR ID
registers. This brings these registers in sync with ARMv8.6 initial spec
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