drivers: adc: stm32: Add function to enable ADC consistently
drivers: adc: stm32: Add function to enable ADC consistently

Use a wrapper for LL_ADC_Enable that also waits for ADRDY if required
by the SoC to make sure it's properly enabled everywhere this is done.

Signed-off-by: Alexander Mihajlovic <86f7e437faa5a7fce15d1ddcb9eaeaea377667b8@abxy.se>

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