dmaengine: dw: don't perform DMA when dmaengine_submit is called

Accordingly to discussion [1] and followed up documentation the DMA controller
driver shouldn't start any DMA operations when dmaengine_submit() is called.

This patch fixes the workflow in dw_dmac driver to follow the documentation.

[1] http://www.spinics.net/lists/arm-kernel/msg125987.html

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

dmaengine: remove ste_dma40 from issue_pending TODO

ste_dma40 now implements issue_pending according to documentation.
Submit adds descriptos to a pending queue with are flushed down to the DMAC
at issue_pending.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

dmaengine: add TODO items for future work on dma drivers

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>