ANDROID: KVM: arm64: Pin host structs for pVMs

In nVHE protected mode the hypervisor sometime needs to read or write to
host-provided data-structures, such as vcpu structs or the kvm struct.

To ensure that the hypervisor can't be tricked by the host into writing
to pages it doesn't own, let's pin the host pages containing those data
structures during the shadow vm creation. This will ensure those pages
remain in a host-shared state for the lifetime of the VM.

Signed-off-by: Quentin Perret <qperret@google.com>
Bug: 209580772
Change-Id: Id11bd6a86754b6a3e0c504b06940df310641357d
Signed-off-by: Will Deacon <willdeacon@google.com>