arm: tegra: implement NVEC driver using tegrai2c.

One thing where we need your help as a I2C maintainer is how to represent an i2c slave device using device-tree. You may remember our discussion in the past from here [1] where you suggested to just make a slave client by its compatible name. Stephen Warren from NVIDIA raised some concerns about this solution because it may not be appropriate in all possible future cases (which is what a proper device-tree representation should take care off). He instead suggested to mark a slave client by adding some flag to the reg property, to be able to handle a situation where both master client and slave client have the same i2c bus address forming a loopback (e.g. for testing purpose) on the same bus. More details here [2].

I hope with this post I can join the different discussions somehow so we are able to find a common sense which is acceptable for all.