ARM: dts: alt: Convert to named i2c-gpio bindings

Commits 7d29f509 ("dt-bindings: i2c: i2c-gpio: Add support for
named gpios") and 05c74778

 ("i2c: gpio: Add support for named
gpios in DT") introduced named i2c-gpio DT bindings, and deprecated the
more error-prone unnamed variant.

Switch to the new bindings, and add the missing GPIO_OPEN_DRAIN I/O
flags, which were implicitly assumed before.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>