dt-bindings: remoteproc: stm32_rproc: update syscon descriptions

Align other syscon descriptions with st,syscfg-m4-state and
st,syscfg-rsc-tbl descriptions by suppressing the cells
description.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Link: https://lore.kernel.org/r/20201014125441.2457-4-arnaud.pouliquen@st.com


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