ASoC: dmaengine: Extend use of chan_names provided in custom DMA config

There are currently two ways to specify custom DMA channel names:
 - through the SND_DMAENGINE_PCM_FLAG_CUSTOM_CHANNEL_NAME flag and
   snd_dmaengine_dai_dma_data data structure,
 - through chan_names field of struct snd_dmaengine_pcm_config.

In order to replace the DAI DMA data method with the custom DMA config
one on non-DT platforms the dmaengine_pcm_new() function is extended
to also consider channel names specified in the custom DMA config.
If both config->chan_names and dma_data->chan_name are provided
the former will be used.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>