tests: drivers: adc: adc_api: update adc_api test

- add nucleo_c071rb overlay file to setup adc node

- The C0 serie has two HSI clock sources, HSI48 and HSI48USB.
To make it simpler and compatible with the existing clock driver,
HSI48 is renamed to HSI (node already present in the stm32c0.dtsi).
HSI48USB will correspond to HSI48.
With SYNC mode, we have an overrun on the ADC, so we configure it
in ASYNC mode.

- Update STM32 HSI macro according to changes

Signed-off-by: Fabrice DJIATSA <fabrice.djiatsa-ext@st.com>