dt-bindings: arm: qcom: Document the Qualcomm qrb4210-rb2 board

Document the Qualcomm qrb4210-rb2 board based on Robotics version
of the Snapdragon SM4250 Soc, i.e. QRB4210.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230411072840.2751813-2-bhupesh.sharma@linaro.org