dts: arm: st: set adc clock source for stm32f2, f4, f7, l1, u5 and wba

STM32L1, U5 and WBA can only have an asynchronous clock source for ADC.
STM32F2, F4 and F7 can only have a synchronous clock source for ADC.
For all these series, it can be defined directly in the dtsi files.

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