power: supply: sbs-battery: add ability to disable charger broadcasts

In certain designs, it is possible to add a battery on a populated i2c
bus without an sbs compliant charger. In that case, the battery will
unnecessarily and sometimes undesirably master the bus trying to write
info in the charger.

It is observed in many occasion that these battery "broadcasts" are even
corrupting other ongoing master to slave communication. I.e. the
multi-master support in the battery is inadequate.

Thankfully, the CHARGER_MODE bit allows designers to disable that SBS
battery behaviour.

This needs to be done once when the battery is first seen on the bus.

Signed-off-by: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
[rebased code]
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>