[RFC] backlight: pwm_bl: do not apply initial PWM state

When we probe the driver, we initialize PWM state with a duty cycle set by default to 0. If the duty cycle was already set by the bootloader, this value will be cleared.

In the case where the PWM drive the backlight of a panel, the panel will turn off first and turn on with the default brightness specified in the device tree.

Thus if the bootloader displayed a splashscreen on the panel, it will disappear when the driver probe.

This behavior may not be expected, instead we could remove the initial call of pwm_apply_state (duty_cycle = 0) and let the driver set first the default brightness.