stm32mp1: use stm32mp_get_ddr_ns_size() function

Instead of using dt_get_ddr_size() and withdrawing the secure and shared
memory areas, use stm32mp_get_ddr_ns_size() function.

Change-Id: I5608fd7873589ea0e1262ba7d2ee3e52b53d9a7d
Signed-off-by: Yann Gautier <yann.gautier@st.com>
2 files changed