This is a preparation of struct dma_mapping_ops unification. We use
map_page and unmap_page instead of map_single and unmap_single.

We will remove map_single and unmap_single hooks in the last patch in
this patchset.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: NMuli Ben-Yehuda <muli@il.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>