arm64: Decode CTR_EL0 via a table

Use the same method to decode CTR_EL0 as for the ID registers. This
will allow us to create a common view over all CPUs.

This will also allow us to create a common view for userspace and the
kernel if we detect a difference on some CPUs, or to handle errata.

Reviewed by: imp
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D47124