dt-bindings: i2c: Add Altera I2C Controller

Add the documentation to support the Altera synthesizable
logic I2C Controller in FPGA.

Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>