spi: dt-bindings: Drop Pratyush Yadav

Emails to Pratyush Yadav bounce ("550 Invalid recipient").  Generic SPI
properties should be maintained by subsystem maintainer (Mark).  Add
recent contributor Vaishnav Achath to the Cadence SPI bindings.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220811063826.7620-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>