dt-bindings: firmware: scm: Add MSM8996 DT bindings

Add SCM DT bindings for Qualcomm's MSM8996 platform.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>