ARM: tegra: Add Tegra30 GMI support

Add a device node for the GMI controller found on Tegra30.

Signed-off-by: Mirza Krak <mirza.krak@gmail.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Colibri T20/T30 on EvalBoard V3.x and GMI-Memory Board
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>