arm64: dts: rockchip: Remove non-existing pwm-delay-us property

arm64: dts: rockchip: Remove non-existing pwm-delay-us property

There is neither a driver that parses this nor a DT binding schema that
documents it, so let's remove from the DTS files that make use of this.

The properties that exist are post-pwm-on-delay-ms and pwm-off-delay-ms,
defined in the pwm-backlight DT binding. If the delays are really needed
then those properties should be used instead.

Brian Norris mentioned though that looking at the first downstream usage
of the pwm-delay-us property for RK3399 Gru systems in ChromiumOS tree,
he couldn't find a spec reference that said that this was really needed.

So perhaps it was unnecessary added and a simple removal would be enough.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/r/20230330231924.2404747-1-javierm@redhat.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>