dt-bindings: pwm: sophgo: add PWM controller for SG2042

Sophgo SG2042 contains a PWM controller, which has 4 channels and
can generate PWM waveforms output.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Link: https://lore.kernel.org/r/d739ea5a1bffcf762248efbe25fae9b9fda6f452.1738737617.git.unicorn_wang@outlook.com


Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>