ASoC: au1x: remove automatic DMA device registration from PSC drivers

The PSC audio drivers (psc-ac97/psc-i2s) register the DMA platform_device
on their own.  This is frowned upon, from now on board code must
register a simple pcm dma platform device for each PSC with sound duties.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>