FROMLIST: KVM: arm64: Expose guest stage-2 pagetable config to debugfs

Make the start level and the IPA bits properties available in the
virtual machine debugfs directory. Make sure that the KVM structure
doesn't disappear behind our back and keep a reference to the KVM struct
while these files are opened.

Bug: 260238318
Bug: 278749606
Link: https://lore.kernel.org/all/20240220151035.327199-7-sebastianene@google.com/


Change-Id: Id1ef86a9cea47693a51a79c6f226f030a6112387
[sebastian: Add a check for is_protected_kvm_enabled]
Signed-off-by: Sebastian Ene <sebastianene@google.com>