ASoC: rsnd: remove non DT support for DMA

Current Renesas Sound driver is based on DeviceTree, and no one is
using this driver from non DT. Non-DT support is no longer needed.
Let's remove it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>