dt-bindings: arm: qcom: Mention that Chromebooks use a different scheme

The qcom.yaml bindings file has a whole description of what the
top-level compatible should look like for Qualcomm devices. It doesn't
match what Chromebooks do, so add a link to the Chromebook docs.

Reported-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220520143502.v4.2.I6418884d8bab6956c7016304f45adc7df808face@changeid