spd: dispatcher for interacting with the Trusty TEE ...

This patch adds the secure payload dispatcher for interacting
with Google's Trusty TEE. Documentation for Trusty can be found
at https://source.android.com/security/trusty

Original authors:
-----------------
* Arve Hjønnevåg <arve@android.com>
* Michael Ryleev <gmar@google.com>

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