This patch saves the TZSRAM context and takes the SoC into System Suspend
from the "_wfi" handler. This helps us save the entire CPU context from
the TZSRAM, before entering System Suspend. In the previous implementation
we missed saving some part of the state machine context leading to an assert
on System Suspend exit.

Change-Id: I4895a8b4a5e3c3e983c245746ea388e42da8229c
Signed-off-by: Harvey Hsieh <hhsieh@nvidia.com>