arm64: dts: qcom: sc7280: Enable keyboard backlight for villager

Villager has a backlit keyboard, enable support for the backlight.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220523123157.v2.2.I3d1b5a109675a0cc90e66a4e0b45cb823edbdee7@changeid