arm64: tegra: Fix GIC400 missing GICH/GICV register regions

GIC400 has full support for virtualization, and yet the tegra186
DT doesn't expose the GICH/GICV regions (despite exposing the
maintenance interrupt that only makes sense for virtualization).

Add the missing regions, based on the hunch that the HW doesn't
use the CPU build-in interfaces, but instead the external ones
provided by the GIC. KVM's virtual GIC now works with this change.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>