ARM: STi: DT: STiH418: Add cpu-release-addr dt property.

To enable SMP when booting via u-boot we need to specify the
newly implemented cpu-release-addr DT property for cores 2 & 3.
Cores 0 & 1 are inherited from stih407-family.dtsi.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>