Rather than having the RPM GLINK channels as the only child of a dummy
top-level rpm-glink node, switch to representing the RPM as remoteproc
like all the other remoteprocs (modem DSP, ...).

This allows assigning additional subdevices to it like the MPM
interrupt-controller or rpm-master-stats.

Tested-by: Konrad Dybcio <konrad.dybcio@linaro.org> # SM6375
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20230531-rpm-rproc-v3-11-a07dcdefd918@gerhold.netSigned-off-by: Bjorn Andersson <andersson@kernel.org>