Platform: stm32l5xx: Create a dedicated stm_tool.py

Since tfm relies on mcuboot upstream, the imgtool stm specific
function used for computing the stm32l5xx board programming
settings is not available on mcuboot upstream. stm_tool.py
implements the computing of board programming settings.

Change-Id: I49059d543806dab198bd18e85be18cf057b82b89
Signed-off-by: Michel Jaouen <michel.jaouen@st.com>
4 files changed