refactor(stm32mp1): remove STM32MP_USE_STM32IMAGE

The code managing legacy boot (without FIP) that was under
STM32MP_USE_STM32IMAGE flag is remove.

Change-Id: I04452453ed84567b0de39e900594a81526562259
Signed-off-by: Yann Gautier <yann.gautier@st.com>
23 files changed