dt-bindings: arm: qcom: Document qcom,sc7280-idp2 board

Document the qcom,sc7280-idp2 board based off sc7280 SoC,
The board is also known as piglin in the Chrome OS builds,
so document the google,piglin compatible as well.

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/1628082199-17002-2-git-send-email-rnayak@codeaurora.org


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