FROMGIT: KVM: arm64: Refcount hyp stage-1 pgtable pages

To prepare the ground for allowing hyp stage-1 mappings to be removed at
run-time, update the KVM page-table code to maintain a correct refcount
using the ->{get,put}_page() function callbacks.

Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211215161232.1480836-3-qperret@google.com
(cherry picked from commit 2ea2ff91
 git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git next)
Bug: 209599700
Change-Id: Ic4ce9177a4381a01e1f2c3b00e9f376e14015718