caf: modules: leds: fix support GPIO-based LED devicetree definitions

[jelledevleeschouwer]

When CONFIG_CAF_LEDS_GPIO was chosen over CONFIG_CAF_LEDS_PWM, an assertion fails that checks whether a gpio-leds compatible node has either 1 or 3 child nodes to define multi-color LEDs. However, most Nordic development boards have 4 leds, which the CAF leds module does not support and hence breaks these builds. This commit adds support for up to a combination of 4 leds in what could be analogous to an RGBW LED. The changes are made as such that as little application code as possible is affected by the change. If user code wants to take full advantage of the full channel color support it will have to redefine the OFF, ON, ON_GO_OFF, BLINK, BLINK2, BREATH, and CLOCK effects since LED_NOCOLOR is only defined for 3 channels.

[NordicBuilder]

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