ARM: tegra: hook tegra_tear_down_cpu function in the PM suspend init function

The tegra_tear_down_cpu was used to cut off the CPU rail for various Tegra
SoCs. Hooking it in the PM suspend init function and making the CPUidle
driver more generic.

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