dt-bindings: pwm: samsung: add exynosautov9 compatible

Add samsung,exynosautov9-pwm compatible string to binding document.

Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Link: https://lore.kernel.org/r/20230718062200.79306-2-jaewon02.kim@samsung.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>