linux-phytec-ti

ARM: trusted_foundations: implement prepare_idle()

Support the prepare_idle() firmware call, which is necessary to properly
support CPU idling.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Stephen Warren <swarren@nvidia.com>