spi: spi-fsl-dspi: Parameterize the FIFO size and DMA buffer size

Get rid of the ifdef for Coldfire and make these hardware
characteristics part of dspi->devtype_data.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Message-Id: <20200302001958.11105-4-olteanv@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>