linux-phytec-ti

dmaengine: omap: add support for returning residue in tx_state method

Add support for returning the residue for a particular descriptor by
reading the current DMA address for the source or destination side of
the transfer as appropriate, and walking the scatterlist until we find
an entry containing the current DMA address.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>