Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn

Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn

Make xen_xlate_map_ballooned_pages work with 64K pages. In that case
Kernel pages are 64K in size but Xen pages remain 4K in size. Xen pfns
refer to 4K pages.

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Tested-by: Julien Grall <julien.grall@arm.com>
(cherry picked from commit 975fac3c4f38e0b47514abdb689548a8e9971081)
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Orabug: 24820937