ARM: tegra: Add GIC for Tegra124

Add a device tree node for the GIC v2 found on the Cortex-A15 CPU
complex of Tegra124. U-Boot doesn't use this but subsequent patches will
add device tree nodes that reference it by phandle.

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