ASoC: ux500_pcm: Extend Device Tree support to deal with DMA data

Soon we will strip out pdata support from the Ux500 set of ASoC drivers.
When this happens it will have to supply a DMA slave_config to the
dmaengine. At the moment a great deal of this comes from pdata via
AUXDATA. We need to become independent of this soon. This patch starts
the process by allocating memory for the associated data structures and
fetches the MSP id used for const struct indexing.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>