There are currently no decisions based on the CPU implementor, variant
or part values for ARM64, and the code to fetch those values was not
compatible with Fuchsia/ARM64.

Bug: chromium:772031
Change-Id: I2305fc7a97d8c0a24bb0ad115447665976e5814a
Reviewed-on: https://chromium-review.googlesource.com/706642Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Rodolph Perfetta <rodolph.perfetta@arm.com>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48472}