FROMGIT: KVM: arm64: pkvm: Unshare guest structs during teardown

Make use of the newly introduced unshare hypercall during guest teardown
to unmap guest-related data structures from the hyp stage-1.

Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211215161232.1480836-15-qperret@google.com
(cherry picked from commit 52b28657
 git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git next)
Bug: 209599700
Change-Id: Ic8ec2c74d3e803e4d5f0df37d144d2c2eb0e9ad3