ARM: tegra: flowctrl: add support for cpu_suspend_enter/exit

The flow controller can help CPU to go into suspend mode (powered-down
state). When CPU goes into powered-down state, it needs some careful
settings before getting into and after leaving. The enter and exit
functions do that by configuring appropriate mode for flow controller.

For Tegra114, the setting is compatible with Tegra30.

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