While arch/*/mem/ptdump handles the kernel pagetable dumping code,
introduce KVM/ptdump to show the guest stage-2 pagetables. The
separation is necessary because most of the definitions from the
stage-2 pagetable reside in the KVM path and we will be invoking
functionality specific to KVM. Introduce the PTDUMP_STAGE2_DEBUGFS config.

When a guest is created, register a new file entry under the guest
debugfs dir which allows userspace to show the contents of the guest
stage-2 pagetables when accessed.

[maz: moved function prototypes from kvm_host.h to kvm_mmu.h]
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://lore.kernel.org/r/20240909124721.1672199-6-sebastianene@google.comSigned-off-by: Marc Zyngier <maz@kernel.org>