KVM: arm64: Maintain per-VM copy of implementation ID regs

Get ready to allow changes to the implementation ID registers by
tracking the VM-wide values.

Signed-off-by: Sebastian Ott <sebott@redhat.com>
Link: https://lore.kernel.org/r/20250225005401.679536-3-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>