Integrate linux-seco-imx/d18-lcd-pwms

Commit: edgehog/bsp/nxp/linux-seco-imx@b73e87a0

[D18] fix lcd backlights pwm-cells error

To support polarity inversion i.MX8MP DT has been changed use 3 pwm-cells. Align lcd backlights pwm by selecting normal polarity.