ASoC: fsl_sai: Enable combine mode soft

The fsl_sai driver calculates the number of pins used and enables
multiple channels if necessary. This means the SAI expects data in
one FIFO per pin. The SDMA engine only services a single FIFO, so
multi pin support doesn't work at all.

This patch enables the software combine mode in chips that support
it. With this the SAI presents only a single FIFO to the outside
and distributes the data into the different FIFOs internally.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20220111081518.982437-1-s.hauer@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>