arm64: dts: qcom: msm8916-samsung-a5u: Add touch key regulator

On the Samsung Galaxy A5 the touch key is supplied by a single fixed
regulator (enabled via GPIO 97) that supplies both MCU and LED.
Add it to the device tree.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20210604172742.10593-3-stephan@gerhold.net


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>