spi: offload trigger: add ADI Util Sigma-Delta SPI driver

Add a new driver for the ADI Util Sigma-Delta SPI FPGA IP core.

This is used to trigger a SPI offload based on a RDY signal from an ADC
while masking out other signals on the same line.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250627-iio-adc-ad7173-add-spi-offload-support-v2-9-f49c55599113@baylibre.com


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