xen/mm: Switch some APIs over to pte_attr_t

xen/mm: Switch some APIs over to pte_attr_t

Several APIs take an architecture-dependent set of flags in an unsigned int,
but this needs to be a wider type to support PPC.

The new type pte_attr_t has been introduced for this purpose, so switch to it
in map_pages_to_xen(), __vmap() and modify_xen_mappings{,_lite}().

No functional change.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Shawn Anastasio <sanastasio@raptorengineering.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>