ASoC: kirkwood: merge struct kirkwood_dma_priv with struct kirkwood_dma_data

Merge these two structures together; nothing other than the I2S and
DMA driver makes use of struct kirkwood_dma_data, and it's not like
struct kirkwood_dma_data is really just used to convey DMA specific
data to the backend; it's more a general shared structure between the
two halves.

This will later allow kirkwood-dma.c and kirkwood-i2s.c to be merged
together.

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