gpio: it8xxx2: open source configuration isn't supported

This makes test of tests/drivers/gpio/gpio_api_1pin happy
on it8xxx2_evb.

Signed-off-by: Dino Li <Dino.Li@ite.com.tw>

drivers/gpio/gpio_ite_it8xxx2.c

@@ -359,6 +359,12 @@ static int gpio_ite_configure(const struct device *dev,
 	__ASSERT(gpio_config->index < GPIO_GROUP_COUNT,
 		"Invalid GPIO group index");
 
+	/* Don't support "open source" mode */
+	if (((flags & GPIO_SINGLE_ENDED) != 0) &&
+	    ((flags & GPIO_LINE_OPEN_DRAIN) == 0)) {
+		return -ENOTSUP;
+	}
+
 	/*
 	 * Select open drain first, so that we don't glitch the signal
 	 * when changing the line to an output.