Tegra186: sanity check power state type

This patch sanity checks the power state type before use,
from the platform's PSCI handler.

Verified with TFTF Standard Test Suite.

Change-Id: Icd45faac6c023d4ce7f3597b698d01b91a218124
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>