ASoC: ti: remove compat dma probing

After running into a link error:

sound/soc/ti/edma-pcm.o:(.rodata+0x18): undefined reference to `edma_filter_fn'

I checked all users of this, and they have new-style 'dma_slave_map' tables,
so none of them should still need it. Removing the associated lines
simplifies the code and avoids the build-time dependency on the
respective dmaengine drivers.

Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>