Both the BQ27421 and BQ27427 have a few preset Chemistry profiles.
For the BQ27421 there exists three variants of the IC, and for the BQ27427,
it can be configured. The chemistry profile among other things includes the
taper voltage, which is used to detect charge termination.
This adds an optional `chemistry-id` config option to the driver. On the
BQ27421, it will confirm that the correct variant of the IC is mounted,
and on the BQ27427, it will configure it with the correct value.
Side note: The reference manual for the BQ27427
(https://www.ti.com/lit/ug/sluucd5/sluucd5.pdf) currently contains some
errors and inconsistencies regarding these registers. The table on page 7
appears to be correct.
Signed-off-by: Tobias Pisani <topisani@hamsterpoison.com>
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