arm/tegra: add support for ventana pinmuxing

Add support for ventana pinmuxing as a seaboard derivative. This is a cut down
version of work done by Jong Kim <jongk@nvidia.com>.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>