feat(plat/st): use FCONF to configure platform

Add required code to support FCONF on STM32MP1 platform.
The new FW_CONFIG DT file will be inside the FIP, and loaded by BL2.
It will be used to configure the addresses where to load other binaries.
BL2 should be agnostic of which BL32 is in the FIP (OP-TEE or SP_min),
so optee_utils.c is always compiled, and some OP-TEE flags are removed.

Change-Id: Id957b49b0117864136250bfc416664f815043ada
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
8 files changed