ANDROID: KVM: arm64: Add protected VM ptdump support

Extend the KVM ptdump support by making sure that it runs under
protected environment. When the guests boot under pKVM, the
stage-2 pagetables of the guests are not controlled by the host
anymore.
Introduce a new hypercall to allow the kernel to extract
pagetable configuration information such as the ipa range
and the start level of the table. Allow the hypercall to
start walking the pagetable inside the hypervisor and output
the descriptors in a shared buffer with the host.

Bug: 337041793
Bug: 353523878
Bug: 357781595
Test: start a protected VM and dump the pagetable by reading
cat /sys/kernel/debug/kvm/*/stage2*
Change-Id: If75184d33679008ae3c0bb79b9d6118185aeb2dd
Signed-off-by: Sebastian Ene <sebastianene@google.com>