drivers/adc: stm32: Don't enable ADC instance by default in driver

ADC_1 peripheral instance was enabled by default in driver.
This is not the usual way to enable peripheral instances, as it
makes board configuration unclear.
Move activation in boards that are declaring ADC support.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
10 files changed