KVM: arm64: Move host page ownership tracking to the hyp vmemmap

We currently store part of the page-tracking state in PTE software bits
for the host, guests and the hypervisor. This is sub-optimal when e.g.
sharing pages as this forces to break block mappings purely to support
this software tracking. This causes an unnecessarily fragmented stage-2
page-table for the host in particular when it shares pages with Secure,
which can lead to measurable regressions. Moreover, having this state
stored in the page-table forces us to do multiple costly walks on the
page transition path, hence causing overhead.

In order to work around these problems, move the host-side page-tracking
logic from SW bits in its stage-2 PTEs to the hypervisor's vmemmap.

Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20241218194059.3670226-5-qperret@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

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