arm64: Update the ID_AA64ISAR0_EL1 fields

While here move to decimal for the _op and _CR definitions to be used
by a future macro to define the register when the assembler doesn't
know about it.

Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D40888

(cherry picked from commit 4182f58172b56f71bfaf2450a0e9cb8b4397bf0a)