dt-bindings: i2c: nvidia,tegra20-i2c: Add Tegra256 I2C compatible

Add compatible for Tegra256 I2C controllers. Tegra256 consists of
8 generic Tegra I2C controllers similar to previous generations.
The parent clock frequency is different in these controllers and
hence the timing parameter values are different from the previous
ones.

Signed-off-by: Akhil R <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

Documentation/devicetree/bindings/i2c/nvidia,tegra20-i2c.yaml

···
           support for 64 KiB transactions whereas earlier chips supported no
           more than 4 KiB per transactions.
         const: nvidia,tegra194-i2c
+      - description: |
+          Tegra256 has 8 generic I2C controllers. The controllers are similar to
+          the previous generations, but have a different parent clock and hence
+          the timing parameters are configured differently.
+        const: nvidia,tegra256-i2c
 
   reg:
     maxItems: 1
···
             contains:
               enum:
                 - nvidia,tegra194-i2c
+                - nvidia,tegra256-i2c
     then:
       required:
         - resets