ARM: dts: imx6*-apalis/-colibri: mark I2C recovery GPIOs as open drain

Since commit d2d0ad2a ("i2c: imx: use open drain for recovery
GPIO") GPIO lib expects this GPIO to be configured as open drain.
Make sure we define this GPIO as open drain in the device tree.
This gets rid of the following warning:
  gpio-81 (scl): enforced open drain please flag it properly in DT/ACPI DSDT/board file

Note that currently the i.MX pinctrl driver does not support
enabling open drain directly, so this patch has no effect in
practice. Open drain is enabled by the fixed pinmux entry.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>