ARM: tegra: Add GIC for Tegra30

Add a device tree node for the GIC found on Tegra30. U-Boot doesn't use
it directly but subsequent patches will add device tree nodes that
reference it by phandle.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>