dt-bindings: mailbox: Add WPSS client index to IPCC

Add WPSS remote processor client index to Inter-Processor Communication
Controller (IPCC) block.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Link: https://lore.kernel.org/r/1619508824-14413-2-git-send-email-sibis@codeaurora.org


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