fuel_gauge: sbs_gauge: Enable MFR ACC write

Update the SBS Gauge driver that implements the fuel_gauge API to implement
a set_property function allowing the writing of an SBS word to the
manufacturer access register per the SBS spec.

Includes an update to the SBS Gauge emulator and SBS fuel gauge tests to
weakly verify the code runs.

Signed-off-by: Aaron Massey <aaronmassey@google.com>