dt: binding: Add Qualcomm WCNSS control binding

This binding describes the control interface for the Qualcomm WCNSS.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>