dt-bindings: spi: dspi: Add S32G support

Document S32G compatible strings. 's32g2' and 's32g3' use the same
driver so 's32g2' must follow 's32g3'. The SPI controller supports
target mode when the "spi-slave" flag is used so add an example.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Ciprian Marian Costea <ciprianmarian.costea@nxp.com>
Signed-off-by: Larisa Grigore <larisa.grigore@nxp.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Link: https://patch.msgid.link/20250522-james-nxp-spi-v2-12-bea884630cfb@linaro.org


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