dt-bindings: pwm: samsung: Do not require interrupts on Exynos SoCs

dt-bindings: pwm: samsung: Do not require interrupts on Exynos SoCs

The bindings required interrupts for all SoCs but actually only the PWM
timer clocksource (for S3C/S5P SoCs) was using them.  This PWM timer
clocksource driver is not used on Exynos SoCs thus the interrupts can be
marked as optional.

Reported-by: Alim Akhtar <alim.akhtar@samsung.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200702155149.12854-1-krzk@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>