KVM: arm64: Allow get_pkvm_hyp_vm() to take a reference to a dying VM

KVM: arm64: Allow get_pkvm_hyp_vm() to take a reference to a dying VM

Now that completion of the teardown path requires a refcount of zero for
the target VM, we can allow get_pkvm_hyp_vm() to take a reference on a
dying VM, which is necessary to unshare pages with a non-protected VM
during the teardown process itself.

Note that vCPUs belonging to a dying VM cannot be loaded and pages can
only be reclaimed from a protected VM (via
__pkvm_reclaim_dying_guest_page()) if the target VM is in the dying
state.

Signed-off-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20260331155056.28220-3-will@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>