spi: s3c64xx: Allow controller-data to be optional

The Samsung SoC SPI driver requires to provide controller-data node
for each of SPI peripheral device nodes.  Make this controller-data node
optional, so DTS could be simpler.

Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Andi Shyti <andi@etezian.org>
Reviwed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220124082347.32747-5-krzysztof.kozlowski@canonical.com