vpci/msix: carve p2m hole for MSIX MMIO regions

vpci/msix: carve p2m hole for MSIX MMIO regions

Make sure the MSIX MMIO regions don't have p2m entries setup, so that
accesses to them trap into the hypervisor and can be handled by vpci.

Commit 042678762 ("x86/iommu: add map-reserved dom0-iommu option to
map reserved memory ranges") added mappings for all the reserved
regions into the PVH Dom0 p2m, and some of those reserved regions
might contain MSIX MMIO regions, hence the need to make sure there are
no mappings established.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>