memory: remove IOMMU MR iommu_set_page_size_mask() callback

memory: remove IOMMU MR iommu_set_page_size_mask() callback

Everything is now in place to use the Host IOMMU Device callbacks
to retrieve the page size mask usable with a given assigned device.
This new method brings the advantage to pass the info much earlier
to the virtual IOMMU and before the IOMMU MR gets enabled. So let's
remove the call to memory_region_iommu_set_page_size_mask in
vfio common.c and remove the single implementation of the IOMMU MR
callback in the virtio-iommu.c

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>