spi: spi-fsl-dspi: set ColdFire to DMA mode

Set DMA transfer mode for ColdFire.

After recent fixes to fsl edma engine, this mode can be used
also for ColdFire, and from some raw mtd r/w tests it definitely
improves the transfer rate, so keeping it selected.

Signed-off-by: Angelo Dureghello <angelo.dureghello@timesys.com>
Link: https://lore.kernel.org/r/20200816094635.1830006-1-angelo.dureghello@timesys.com


Signed-off-by: Mark Brown <broonie@kernel.org>