Platform: Add the support of stm32l5xx

- nucleo_l552ze_q and disco_l562qe boards supported
and build with gnuarm compiler.
- dummy driver for nvm counter,
- mcuboot config overwrite only and 2 images,
- timer not supported
- icache ip not activated

Change-Id: I6c87662ae26fc6552e0b65f35000cfc73735fd21
Signed-off-by: Michel Jaouen <michel.jaouen@st.com>