spi: dt-bindings: snps,dw-apb-ssi: Add compatible for SOPHGO SG2042 SoC

Sophgo SG2042 ships an SPI controller [1] compatible with the Synopsys
DW-SPI IP. Add SoC-specific compatible string and use the generic one
as fallback.

Link: https://github.com/sophgo/sophgo-doc/blob/main/SG2042/TRM/source/SPI.rst

 [1]

Signed-off-by: Zixian Zeng <sycamoremoon376@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250425-sfg-spi-v6-2-2dbe7bb46013@gmail.com


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