drivers: fuel_gauge: sbs_gauge: Add support for buffer registers

The buffer registers (chemistry, manufacturer name, device name) were
not implemented. Implemented by adding a new api interface for
retrieving buffer properties. fuel_gauge_get_block_property has been
added, and uses a memory buffer allocated in the app in order to
store the fuel gauge information.

Signed-off-by: Peter Rowley <perowle@microsoft.com>