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 d15e805b179cfee589c0c624ae4dddf771042e9b.