dmaengine: apple-admac: Allocate cache SRAM to channels

There's a previously unknown part of the controller interface: We have
to assign SRAM carveouts to channels to store their in-flight samples
in. So, obtain the size of the SRAM from a read-only register and divide
it into 2K blocks for allocation to channels. The FIFO depths we
configure will always fit into 2K.

(This fixes audio artifacts during simultaneous playback/capture on
multiple channels -- which looking back is fully accounted for by having
had the caches in the DMA controller overlap in memory.)

Fixes: b127315d ("dmaengine: apple-admac: Add Apple ADMAC driver")
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20221019132324.8585-2-povik+lin@cutebit.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>