i2c: tegra: Add i2c support

Adds I2C bus driver for nVidia Tegra SoCs.  Tegra includes 4 I2C
controllers, one of which is inside the Dynamic Voltage Controller
and has a slightly different register map.

Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>