dt-bindings: i2c: gpio: Add properties for dealing with write-only SDA/SCL w/o pullup

There are slave devices that understand I2C but have read-only SDA and
SCL. Examples are FD650 7-segment LED controller and its derivatives.
Typical board designs don't even have a pull-up for both pins.
Therefore add properties for not using open-drain. For write-only SCL
we have a property already, add one for write-only SDA.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>