scripts: serie_update.py: add systematic compilation of '_hal_rcc_ex.c'

Add systematic compialtion of '..._hal_rcc_ex.c' in 'CMakeLists.txt'
generation. There is more and more dependence of HAL IP to
'..._hal_rcc_ex.c'

Signed-off-by: Alexandre Bourdiol <alexandre.bourdiol@st.com>