dt-bindings: mailbox: qcom-ipcc: Add NSP1 client

Add a client for the NSP1 found in some recent Qualcomm platforms.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220629041438.1352536-3-bjorn.andersson@linaro.org