feat(st): add a configuration without AARCH32_SP

On STM32MP15, we can choose either SP_MIN or OP-TEE as BL32. BL2 can be
compiled without the knowledge of the BL32 used, it is detected at
runtime. A new configuration is added for this BL2 compilation. It
follows the discussion for a patch checking AARCH32_SP:
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/22558

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I735b6128139121f82b0824bc4516b7b884abfb5b
3 files changed