staging: android: ion: Add support to force DMA sync

Currently ION doesn't always DMA sync the memory it allocates and
it doesn't always do a DMA sync in response to a begin/end cpu access
call.

Add support in ION, via the CONFIG_ION_FORCE_DMA_SYNC config, to force a
DMA sync when ION memory is allocated and when calls to begin/end cpu
access are made.

This makes it possible to force ION's cache maintenance to behave like
it did on the previous version of ION.

Change-Id: Ifb2da086e46647697129c20206b24e249092d7f7
Signed-off-by: Liam Mark <lmark@codeaurora.org>