ARM: tegra: functions to access the flowcontroller

Introduce some functions to write to the flowcontroller registers. The
flowcontroller controls CPU sleepstates and wakeup.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>