The published errata specify the maximum allowed SPI frequency to be
max 85% of (FSYSCLK/2). So there's no need to track known bad clock
settings in the driver. As the setup of known good values is a bit
tricky, keep them.

Link: https://lore.kernel.org/r/20210128104644.2982125-4-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>