STM32G4 uses v2 ADC but has EXTSEL and ALIGN fields modified, rather
than making a v3 ADC for these minor changes, the definitions have been
moved to the chip specific headers, so that the common code can work for
G4 onwards.
L4 and F3 actually have the same bits to write in the same order, but F3 hides
the name of the deep power down bit. Keep the like that for now, but there's a
standard API for enabling and disabling the regulator.