dt-bindings: Add new chips to bq25890 binding documentation

Add bq25892, bq25895 and bq25896 to list of supported device IDs in the
bq25890 DT binding document.

Signed-off-by: Yauhen Kharuzhy <jekhor@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>