feat(plat/st): add helper to save boot interface

Some parameters from BootROM boot context can be required after boot.
To save space in SYSRAM, this context can be overwritten during images
load sequence. The needed information (here the boot interface) is
then saved in a local variable.

Change-Id: I5e1ad4630ccf78480f415a0a83939005ae67729e
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
2 files changed