dmaengine: dw-edma: Fix invalid interleaved xfers semantics

The interleaved DMA transfer support added in commit 85e7518f
("dmaengine: dw-edma: Add device_prep_interleave_dma() support") seems
contradicting to what the DMA-engine defines. The next conditional
statements:
	if (!xfer->xfer.il->numf)
		return NULL;
	if (xfer->xfer.il->numf > 0 && xfer->xfer.il->frame_size > 0)
		return NULL;
basically mean that numf can't be zero and frame_size must always be zero,
otherwise the transfer won't be executed. But further the transfer
execution method takes the frames size from the
dma_interleaved_template.sgl[] array for each frame. That array in
accordance with [1] is supposed to be of
dma_interleaved_template.frame_size size, which as we discovered before
the code expects to be zero. So judging by the dw_edma_device_transfer()
implementation the method implies the dma_interleaved_template.sgl[] array
being of dma_interleaved_template.numf size, which is wrong. Since the
dw_edma_device_transfer() method doesn't permit
dma_interleaved_template.frame_size being non-zero then actual multi-chunk
interleaved transfer turns to be unsupported even though the code implies
having it supported.

Let's fix that by adding a fully functioning support of the interleaved
DMA transfers. First of all dma_interleaved_template.frame_size is
supposed to be greater or equal to one thus having at least simple linear
chunked frames. Secondly we can create a walk-through all over the chunks
and frames just by initializing the number of the eDMA burst transactios
as a multiple of dma_interleaved_template.numf and
dma_interleaved_template.frame_size and getting the frame_size-modulo of
the iteration step as an index of the dma_interleaved_template.sgl[]
array. The rest of the dw_edma_device_transfer() method code can be left
unchanged.

[1] include/linux/dmaengine.h: doc struct dma_interleaved_template

Fixes: 85e7518f ("dmaengine: dw-edma: Add device_prep_interleave_dma() support")
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-By: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>