drivers: counter: stm32 timer counter driver LL prototype

Adapt the stm32 counter-timer driver to the stm32_ll function
prototype. Some stm32 families have
LL_TIM_OC_GetCompareCHx(TIM_TypeDef some others have
LL_TIM_OC_GetCompareCHx(const TIM_TypeDef.
This will fix compilation warning.
Adds the macro for stm32L0 16bit timers.

Signed-off-by: Francois Ramu <francois.ramu@st.com>