dma-buf: add dma_data_direction to unmap dma_buf_op

Some exporters may use DMA map/unmap APIs in dma-buf ops, which require
enum dma_data_direction for both map and unmap operations.

Thus, the unmap dma_buf_op also needs to have enum dma_data_direction as
a parameter.

Reported-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>