dt-bindings: pwm: samsung: add exynosautov920 compatible

Add samsung,exynosautov920-pwm compatible string to binding document.

Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20231115095609.39883-6-jaewon02.kim@samsung.com


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