ASoC: OMAP: HDMI: Create a structure for private data of the CPU DAI

Create a struct hdmi_priv to store the relevant data of the CPU DAI
driver. As more data is added to the driver, having all the data
in the same location eases its handling. At the moment, only the DMA
configuration parameters are included in the structure.

Also, the required memory is allocated using devm_kzalloc rather than
using a static global variable.

Signed-off-by: Ricardo Neri <ricardo.neri@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>