stm32mp1: move check_header() to common code

This function can be used on several stm32mp devices, it is then moved in
plat/st/common/stm32mp_common.c.

Change-Id: I862debe39604410f71a9ddc28713026362e9ecda
Signed-off-by: Yann Gautier <yann.gautier@st.com>
3 files changed