dt-bindings: i2c: tegra: Document Tegra210 VI I2C

The Tegra210 features an instance of the Tegra I2C controller that is
part of the host1x domain and typically used for camera use-cases. It
uses pretty much the same programming model but the registers are laid
out differently.

Signed-off-by: Thierry Reding <treding@nvidia.com>