[PATCH] spi: sun6i: Set SPI mode in prepare_message

[Kevin Mehall]

I tested with `spi-cs-setup-delay-ns = <1000000>;` and a hardware CS in the
device tree, and confirmed the suspected second bug: without this patch, the
first transfer after autosuspend ignores the setup delay.

> I do see that the driver uses a reset controller over suspend, are you
> sure that setup() will be called again on resume?

SUN6I_TFR_CTL_REG is indeed being reset after autosuspend because the above bug
reoccurs after a few seconds of inactivity. I am not sure if setup() is running on
resume because the datasheet reset value of SUN6I_TFR_CTL_CS_LEVEL is the same
as what would be written. Either way, it's moot if we set all CS-related bits in
the same register write.

I've moved the line that sets SUN6I_TFR_CTL_CS_MANUAL into sun6i_spi_set_cs()
rather than into sun6i_spi_prepare_message() as a separated commit in a new patch
series:
https://lore.kernel.org/linux-spi/20260423174001.2797797-1-km@kevinmehall.net/