ARM: tegra: add low level code for Tegra114 cluster power down

When the CPU cluster power down, the vGIC is powered down too. The
flow controller needs to monitor the legacy interrupt controller to
wake up CPU. So setting up the appropriate wake up event in flow
controller.

Signed-off-by: Joseph Lo <josephl@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>