Missing 'label' on most nodes with 'compatible = "pwm-leds"'

[ulfalizer]

dts/bindings/led/pwm-leds.yaml says that any node with that binding must have a label property, but only a few nodes with compatible = "pwm-leds" have a label property.

List for reference:

$ git grep pwm-leds
boards/arm/hexiwear_k64/hexiwear_k64.dts:               compatible = "pwm-leds";
boards/arm/nucleo_l496zg/nucleo_l496zg.dts:             compatible = "pwm-leds";
boards/riscv32/hifive1/hifive1.dts:             compatible = "pwm-leds";
dts/bindings/device_node.yaml.template:# Here's an example for a pwm-leds binding in which the child nodes
dts/bindings/led/pwm-leds.yaml:      constraint: "pwm-leds"

This leads to failures in #17660, which turns missing category: required properties into an error.

Not familiar enough with how this is used to know what the proper solution is. A quickfix would be to make label optional instead in the binding (category: optional).

[ulfalizer]

CC @galak

[ulfalizer]

@ioannisg
Note that these are part of fixing an entire class of issue, so don't get hung up on the individual fixes. It'd be nice to get them all fixed soonish, even if each one is low-prio in itself.