gpio: aspeed: Add open-source and open-drain support

As per the datasheet, manage the IO and value states to implement
open-source/open-drain, but do this by falling back to gpiolib's
emulation.

This commit simply makes the behaviour explicit for clarity, rather than
relying on the implicit return of -ENOTSUPP to trigger the emulation.
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-aspeed.c

@@ -761,6 +761,10 @@ static int aspeed_gpio_set_config(struct gpio_chip *chip, unsigned int offset,
 			param == PIN_CONFIG_BIAS_PULL_DOWN ||
 			param == PIN_CONFIG_DRIVE_STRENGTH)
 		return pinctrl_gpio_set_config(offset, config);
+	else if (param == PIN_CONFIG_DRIVE_OPEN_DRAIN ||
+			param == PIN_CONFIG_DRIVE_OPEN_SOURCE)
+		/* Return -ENOTSUPP to trigger emulation, as per datasheet */
+		return -ENOTSUPP;
 
 	return -ENOTSUPP;
 }