feat(st): add build configs for STM32MP2

Add configuration to build STM32MP2 platform. The default config uses
OP-TEE as SPD, a DDR4, and uses eMMC or SD-card for boot device.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Id6b3c6fcd09ddfd87d2780c1da55b07ebf52a7ae
3 files changed