stm32mp1: use functions to retrieve some peripheral addresses

stm32mp1: use functions to retrieve some peripheral addresses

PWR, RCC, DDRPHYC & DDRCTRL addresses can be retrieved from device tree.
Platform asserts the value read from the DT are the SoC addresses.

Change-Id: I43f0890b51918a30c87ac067d3780ab27a0f59de
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
Signed-off-by: Nicolas LE BAYON <nicolas.le.bayon@st.com>