mm/huge_memory: use normal_or_softleaf_folio_pmd() in the PMD split path

PMD 拆分路径改用 normal_or_softleaf_folio_pmd() 一次取 folio，并用 vma_has_deposited_pgtable() 判断 deposit，与 zap_huge_pmd() 分类一致，移除 vma_is_mm_managed()。