Review pins mapping

Use the related user manual to define the best pins mapping:
UM1956: STM32 Nucleo-32 board

It is also possible to check the equivalent file for mbed os:
https://developer.mbed.org/platforms/ST-Nucleo-F207ZG/

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm