FROMGIT: KVM: arm64: Implement kvm_pgtable_hyp_unmap() at EL2

Implement kvm_pgtable_hyp_unmap() which can be used to remove hypervisor
stage-1 mappings at EL2.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211215161232.1480836-6-qperret@google.com
(cherry picked from commit 82bb0244
 git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git next)
Bug: 209599700
Change-Id: I7c8dababccaa31a7b6d90977d583c8c0f8b8d47a