dt-bindings: arm: qcom: Document SM4450 SoC and boards

Document the SM4450 SoC binding and also the boards using it.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Tengfei Fan <quic_tengfan@quicinc.com>
Link: https://lore.kernel.org/r/20230731080043.38552-3-quic_tengfan@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>