plat/st: Add USB boot

Handle boot from USB with DFU and STM32CubeProgammer with mmap io.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Change-Id: I6fa7e46c52dcbb5e5ccd162c26eed16cd1e148a7
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/177375


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>
Tested-by: Yann GAUTIER <yann.gautier@st.com>