feat(st): disable authentication based on part_number

STM32MP15xA and STM32MP15xD chip part numbers don't
support the secure boot.
All functions linked to secure boot must not be used
and signed binaries are not allowed on such chip.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I5b85f322f5eb3b64415e1819bd00fb2c99f20695