This is system level code, and should only depend on the host page
size, not the target page size.

Note that HOST_PAGE_SIZE is misleadingly lead and is really aligning
to both host and target page size. Hence it's replacement with
REAL_HOST_PAGE_SIZE.
Signed-off-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Tested-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>