Add a field with the tx/rx register address to the DMA parameters
structure, and set it to the correct address during device
initialization.

This address used to be hardcoded in the DMA controller driver, it now
needs to be explicitly figured out by the device driver.
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>