i2c: tegra: Add the fifth bus on SoC with more than 4 buses

Create the i2c adapter object for the fifth bus on SoC with more than
4 buses. This allow using all the bus available on T30.

Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de>
Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>