dts: arm: st: f0: Refactor stm32f0xx inclusion tree

Modify the successive dtsi include to better reflect the underlying
structure of the F0 family.
There are two main subfamilies: STM32F0x0 on one side, and STM32F0x1, x2
and x8 on the other

Signed-off-by: Guillaume Gautier <guillaume.gautier-ext@st.com>