ion: fix dma APIs

__dma_page_cpu_to_dev is a private ARM api that is not available
on 3.10 and was never available on other architectures.  We can
get the same behavior by calling dma_sync_sg_for_device with a
scatterlist containing a single page.  It's still not quite a
kosher use of the dma apis, we still conflate physical addresses
with bus addresses, but it should at least compile on all
platforms, and work on any platform that doesn't have a physical
to bus address translation.

Change-Id: I8451c2dae4bf85841015c016640684ac28430a5a
Signed-off-by: Colin Cross <ccross@android.com>