ASoC: apple: mca: Postpone requesting of DMA channels

Move the requesting of DMA channels further down from 'probe' to
'pcm_new'. This is to spare the allocated DMA channel resources as we
typically only ever use one or two of the clusters for PCM streaming.
Before we would request DMA channels for all clusters.

(This is prompted by a change in the Audio DMA Controller driver, which
will now be allocating cache SRAM to channels.)

Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20220905074030.1293-1-povik+lin@cutebit.org
Signed-off-by: Mark Brown <broonie@kernel.org>