I2C signals SDA/SCL are a bit different, they need to be pull-up and
open-drain (so to support multiple I2C devices).
Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Signed-off-by: Eric Miao <eric.miao@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>