arm64: tegra: Add AGIC node for Tegra210

Populate the Audio GIC (AGIC) node for Tegra210. This interrupt
controller is used by the Audio Processing Engine to route interrupts
to the main CPU interrupt controller. The AGIC is based on the ARM
GIC400 and so uses the clock name "clk" as specified by the GIC binding
document for GIC400 devices.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>