arm64: dts: qcom: sm7225-fairphone-fp4: Configure WLED

WLED is used for controlling the display backlight on this phone, so
configure the node and enable it.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211229170358.2457006-5-luca.weiss@fairphone.com