feat(st): introduce new platform STM32MP2

This new STMicroelectronics SoC is based on a dual Cortex-A35.
For the moment, only BL2 is compiled with the common parts for ST
platforms.

Change-Id: I1bc4e6835dba4230359ea9b26d736791e27258aa
Signed-off-by: Yann Gautier <yann.gautier@st.com>
8 files changed