m68k: Provide dma_alloc_attrs()/dma_free_attrs()

m68k: Provide dma_alloc_attrs()/dma_free_attrs()

Since commit 0049fb2603b7afb1080776ee691dfa5a3d282357 ("OMAPFB: use
dma_alloc_attrs to allocate memory") we have one non-arch user of
dma_{alloc,free}_attrs().

Hence provide these functions, as wrappers around
dma_{alloc,free}_coherent().

Note that most architectures do it the other way around. But as so far
m68k doesn't support the attributes at all, our solution should generate
smaller code.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>