ARM: dts: Remove "spidev" nodes

"spidev" is not a real device, but a Linux implementation detail. It has
never been documented either. The kernel has WARNed on the use of it for
over 6 years. Time to remove its usage from the tree.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211217221232.3664417-1-robh@kernel.org

'
Reviwed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>