fpga: ice40-spi: Add SPI device ID table

Currently autoloading for SPI devices does not use the DT ID table, it uses
SPI modalises. Supporting OF modalises is going to be difficult if not
impractical, an attempt was made but has been reverted, so ensure that
module autoloading works for this driver by adding a SPI ID table.

Fixes: 96c8395e ("spi: Revert modalias changes")
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>