ARM: dts: STiH407-family: update rproc node names to avoid conflict

The two st231-rproc nodes have the same name; Due to that it was
impossible to distinguish them in remoteproc sysfs and debugfs
interface.
This patch provides them a name related to their functionality.

Signed-off-by: Loic Pallardy <loic.pallardy@st.com>