tests: Enable sbs_gauge driver native_posix

The SBS Gauge drivers tests only executed directly on hardware before. In
addition, the tests were flawed as they were only testing that behavior was
failing.

Enable the SBS Gauge emulator and fix driver tests so they execute
correctly.

TEST=twister -T tests/drivers/sensor/sbs_gauge

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