boards: arm: stm32wb55 nucleo board has low power states

The low power states 0∕1∕2 are added to the stm32wb55rg
nucleo board, with default min residency values.
The substate-id is mapping the same Zephyr power state.
They correspond to the stm32wb55 low power stop0/1/2 modes.

Signed-off-by: Francois Ramu <francois.ramu@st.com>
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