dt-bindings: arm: qcom: Document sc7280 SoC and board

Document the sc7280 SoC and the IDP board bindings

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1615461961-17716-2-git-send-email-rnayak@codeaurora.org


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