intel-iommu: introduce vtd_page_walk_info
    
    During the recursive page walking of IOVA page tables, some stack
    variables are constant variables and never changed during the whole page
    walking procedure.  Isolate them into a struct so that we don't need to
    pass those contants down the stack every time and multiple times.
    
    CC: QEMU Stable <qemu-stable@nongnu.org>
    Signed-off-by: Peter Xu <peterx@redhat.com>
    Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    (cherry picked from commit fe215b0cbb8c1f4b4af0a64aa5c02042080dd537)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>