ANDROID: KVM: arm64: pkvm: Add MMIO guard infrastructure

Introduce the infrastructure required to identify an IPA region
that is expected to be used as an MMIO window.

This include mapping, unmapping and checking the regions. Nothing
calls into it yet, so no expected functional change.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Bug: 209580772
Change-Id: I227eaa28b98e067e3daae4f9e1071eb37a6761cc
Signed-off-by: Will Deacon <willdeacon@google.com>