ec/starlabs: Guard Max Charge in Kconfig

Guard Max Charge EC write in Kconfig so it's only used on
platforms that support it.

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Change-Id: I7be39cd9543c8253d53070950edc6908a21e864a
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62123
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Andy Pont <andy.pont@sdcsystems.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/ec/starlabs/merlin/Kconfig

@@ -44,6 +44,13 @@ config EC_STARLABS_FAN
 	help
 	  Select if the mainboard has a fan.
 
+config EC_STARLABS_MAX_CHARGE
+	bool
+	default n
+	depends on EC_STARLABS_ITE
+	help
+	  Select if the mainboard supports limiting the maximum charge of the battery.
+
 config EC_STARLABS_MERLIN
 	bool "Use open-source Merlin EC Firmware"
 	default n

src/ec/starlabs/merlin/ec.c

@@ -130,11 +130,12 @@ static void merlin_init(struct device *dev)
 		CHARGE_60
 	};
 
-	ec_write(ECRAM_MAX_CHARGE,
-		get_ec_value_from_option("max_charge",
-					 0,
-					 max_charge,
-					 ARRAY_SIZE(max_charge)));
+	if (CONFIG(EC_STARLABS_MAX_CHARGE))
+		ec_write(ECRAM_MAX_CHARGE,
+			get_ec_value_from_option("max_charge",
+						 0,
+						 max_charge,
+						 ARRAY_SIZE(max_charge)));
 
 	/*
 	 * Fan Mode