arm64/mm: Override arch_wants_pte_order()

Define an arch-specific override of arch_wants_pte_order() so that when
anon_orders=recommend is set, large folios will be allocated for
anonymous memory with an order that is compatible with arm64's HPA uarch
feature.

Reviewed-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>