Enable TRUSTED_BOARD_BOOT. This change removes calls to
stm32mp_check_header() and stm32mp_auth_image() when boot images
are loaded since images are now verified from the authentication
framework.

Change-Id: Iec5b645e1581543c99ae59bdb4dd033c577f2295
Signed-off-by: Nicolas Toromanoff <nicolas.toromanoff@st.com>
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>