tegra: i2c: Initialise I2C on Nvidia boards

This enables I2C on all Nvidia boards including Seaboard and
Harmony.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>