spi: add multi_lane_mode field to struct spi_transfer

spi: add multi_lane_mode field to struct spi_transfer

Add a new multi_lane_mode field to struct spi_transfer to allow
peripherals that support multiple SPI lanes to be used with a single
SPI controller.

This requires both the peripheral and the controller to have multiple
serializers connected to separate data lanes. It could also be used with
a single controller and multiple peripherals that are functioning as a
single logical device (similar to parallel memories).

Acked-by: Nuno Sá <nuno.sa@analog.com>
Acked-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20260123-spi-add-multi-bus-support-v6-4-12af183c06eb@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>