ARM: dts: rockchip: set PWM delay backlight settings for Veyron

For veyron the binding should provide both PWM timings, the delay between
you enable the PWM and set the enable signal, and the delay between you
disable the PWM signal and clear the enable signal. Update the binding
accordingly, in this case the panels connected to the veyron boards have
a symmetric power sequence, hence the same value is used.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>