ARC backend for dma_sync_single_for_(device|cpu) was broken as it was
not honoring the @dir argument and simply forcing it based on the call:
 - arc_dma_sync_single_for_device(dir) assumed DMA_TO_DEVICE (cache wback)
 - arc_dma_sync_single_for_cpu(dir) assumed DMA_FROM_DEVICE (cache inv)

This is not true given the DMA API programming model and has been
discussed here [1] in some detail.

Interestingly while the deficiency has been there forever, it only started
showing up after 4.17 dma common ops rework, commit a8eb92d0
("arc: fix arc_dma_{map,unmap}_page") which wired up these calls under the
more commonly used dma_map_page API triggering the issue.

[1]: https://lkml.org/lkml/2018/5/18/979
Fixes: commit a8eb92d0 ("arc: fix arc_dma_{map,unmap}_page")
Cc: stable@kernel.org # v4.17+
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: reworked changelog]