remoteproc: dt: Provide bindings for ST's Remote Processor Controller driver

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>