ARM: tegra: tamonten: Add DDC/PTA pinmux

This commit allows the I2C2 controller on Tegra20 to be routed either to
the DDC or the PTA pin group at runtime. On Tamonten this allows the I2C
bus to be used for the DDC of the HDMI connector or to access I2C chips
on the carrier board.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>