xen/virtio: Convert PAGE_SIZE/PAGE_SHIFT/PFN_UP to Xen counterparts

Currently, a grant ref is always based on the Xen page granularity
(4KB), and guest commonly uses the same page granularity.
But the guest may use a different page granularity (i.e 64KB).
So adopt the code to be able to deal with it.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Link: https://lore.kernel.org/r/20221008151013.2537826-3-olekstysh@gmail.com


Signed-off-by: Juergen Gross <jgross@suse.com>