ARM: dts: stm32: update stm32mp151 for remote proc synchronization support

Two backup registers are used to store the Cortex-M4 state and the resource
table address.
Declare the tamp node and add associated properties in m4_rproc node
to allow Linux to attach to a firmware loaded by the first boot stages.

Associated driver implementation is available in commit 9276536f
("remoteproc: stm32: Parse syscon that will manage M4 synchronisation").

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>