Enabling a higher channel of the internal ADC had the effect of
initializing the lower ones as well. Now that happens only if
actively requested.
Also, the functions for handling the internal ADC did not follow
the typical naming used by comparable modules for the same arch
and were renamed for coherence. Informational logging calls were
also made slightly more useful and discernible in case of having
multiple ADCs.
Signed-off-by: Niccolò Maggioni <nicco.maggioni+nuttx@gmail.com>
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