ANDROID: KVM: arm64: Add host stage-2 ptdump support

Allow the host stage-2 pagetables to be dumped to
debugfs using ptdump. When pKVM is enabled, register
new virtual file entries with debugfs and use the
previously introduced HVC(__pkvm_ptdump_handle) to
walk the host stage-2 pagetables and print the
descriptors to a shared buffer.

Bug: 337041793
Bug: 353523878
Bug: 357781595
Change-Id: Ib28e18a9a466c8c91850cda2922a12305f722e46
Signed-off-by: Sebastian Ene <sebastianene@google.com>