echoplayer: pcm: increase SAI FIFO buffer depth
Change the SAI FIFO threshold so that it is always
kept topped up at maximum; DMA needs to do single
transfers to the peripheral now. Ignore FEIF errors
since they seem to occur constantly with this setup
(though it's not exactly clear why this happens).
FEIF only indicates that the SAI made a DMA request
while the DMA FIFO is empty, which isn't a fatal error.
The DMA channel will simply service the request when
it is ready.
Keeping the SAI FIFO constantly full increases the
overall timing margin before underrun so losing the
FEIF info isn't a big deal in practice.
Change-Id: I16eb1cbb17039db76938bd86c4921b8060c83556
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