ARM: dts: qcom: apq8074-dragonboard: add onboard leds

The dragonboard as three LEDs: red, green and blue. Add corresponding
description.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230531012627.3813060-2-dmitry.baryshkov@linaro.org