Fix write access fault when host npt is mapped read-only.
In this case let the host handle the #NPF.
Apply host p2mt to hap-on-hap pagetable entry.
This fixes the l2 guest graphic display refresh problem.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>
CC: Tim Deegan <tim@xen.org>


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