ARM: dts: imx: bx50v3: i2c GPIOs are open drain

Explicitly mark I2C GPIOs as open drain to fix the following
kernel message being printed:

enforced open drain please flag it properly in DT/ACPI DSDT/board file

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>