feat(st): add USB and UART build config

Add build configurations for USB and UART use-cases. Those are used
when programming the boot device.
Those missing configurations were highlighted with compilation issues:
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/16973

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I223496c9c3dfe51f203d7e51f83c565fbd13f9a4
4 files changed