dt-bindings: arm: qcom: Document asus,sparrow device

Document the ASUS ZenWatch 2 ("sparrow") which is a smartwatch based on
Snapdragon 400 SoC.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220226101939.1011551-1-luca@z3ntu.xyz