KVM: arm64: Add debugfs file for guest's ID registers

Debugging ID register setup can be a complicated affair. Give the
kernel hacker a way to dump that state in an easy to parse way.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240214131827.2856277-27-maz@kernel.org


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