ASoC: omap-mcbsp: Simplify DMA configuration

Configure the DMA request line, port address, and stream name at
probe time instead of every time we start a stream.
These settings are static in the system.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>