mm: hugetlb: move mpol interpretation out of alloc_buddy_hugetlb_folio_with_mpol()

Move memory policy interpretation out of alloc_buddy_hugetlb_folio_with_mpol() and into alloc_hugetlb_folio() to separate reading and interpretation of memory policy from actual allocation. This will later allow memory policy to be interpreted outside of the process of allocating a hugetlb folio entirely. This opens doors for other callers of the HugeTLB folio allocation function, such as guest_memfd, where memory may not always be mapped and hence may not have an associated vma. Introduce struct mempolicy_interpreted to hold all the components of an interpreted memory policy. Rename alloc_buddy_hugetlb_folio_with_mpol() to alloc_buddy_hugetlb_folio() since the function no longer interprets memory policy. No functional change intended.

ATAckerley Tng committed 4 months ago