power: supply: bq25890_charger: Add the BQ25896 part

The BQ25896 is almost identical to the BQ25890.

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>