spi: spi-axi-spi-engine: remove usage of delay_usecs

The 'delay_usecs' field was handled for backwards compatibility in case
there were some users that still configured SPI delay transfers with
this field.

They should all be removed by now.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210308145502.1075689-2-aardelean@deviqon.com


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