power: supply: sbs-battery: cache constant string properties

Currently sbs-battery supports three string properties -
manufacturer, model_name, and chemistry. Buffers for those
properties are currently defined as global variables.

This patch moves those global variables into struct sbs_info
and cache/reuse them as they are all constant values.

Signed-off-by: Ikjoon Jang <ikjn@chromium.org>
Tested-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>