fuel_gauge: Implement sbs gauge read for mfr acc

Implement and weakly test fetching the manufacturer access word from an SBS
compatible fuel gauge.

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

drivers/fuel_gauge/sbs_gauge/sbs_gauge.c

@@ -69,6 +69,10 @@ static int sbs_gauge_get_prop(const struct device *dev, struct fuel_gauge_get_pr
 		rc = sbs_cmd_reg_read(dev, SBS_GAUGE_CMD_AVG_TIME2FULL, &val);
 		prop->value.runtime_to_empty = val;
 		break;
+	case FUEL_GAUGE_SBS_MFR_ACCESS:
+		rc = sbs_cmd_reg_read(dev, SBS_GAUGE_CMD_MANUFACTURER_ACCESS, &val);
+		prop->value.sbs_mfr_access_word = val;
+		break;
 	case FUEL_GAUGE_STATE_OF_CHARGE:
 		rc = sbs_cmd_reg_read(dev, SBS_GAUGE_CMD_ASOC, &val);
 		prop->value.state_of_charge = val;

subsys/emul/i2c/emul_sbs_gauge.c

@@ -53,6 +53,7 @@ static int emul_sbs_gauge_reg_read(const struct emul *target, int reg, int *val)
 	ARG_UNUSED(target);
 
 	switch (reg) {
+	case SBS_GAUGE_CMD_MANUFACTURER_ACCESS:
 	case SBS_GAUGE_CMD_VOLTAGE:
 	case SBS_GAUGE_CMD_AVG_CURRENT:
 	case SBS_GAUGE_CMD_TEMP:

tests/drivers/fuel_gauge/sbs_gauge/src/test_sbs_gauge.c

@@ -123,6 +123,9 @@ ZTEST_F(sbs_gauge_new_api, test_get_props__returns_ok)
 		{
 			.property_type = FUEL_GAUGE_CYCLE_COUNT,
 		},
+		{
+			.property_type = FUEL_GAUGE_SBS_MFR_ACCESS,
+		},
 	};
 
 	int ret = fixture->api->get_property(fixture->dev, props, ARRAY_SIZE(props));