Revert "mm: simplify find_vma_prev() commit 297c5eee37 ("mm: make the vma list be doubly linked") added the vm_prev member to vm_area_struct. We can simplify find_vma_prev() by using it. Also, this change helps to improve page fault performance because it has stronger locality of reference."

This reverts commit b9d03ce9ea5ed6c8038799aff2cb0cfa77ff209b.