Get from the DT the syncon to probe the state of the remote processor
and the location of the resource table.

Mainly based on the work published by Arnaud Pouliquen [1].

[1]. https://patchwork.kernel.org/project/linux-remoteproc/list/?series=239877Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Loic Pallardy <loic.pallardy@st.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200714200445.1427257-6-mathieu.poirier@linaro.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>