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>

Tegra: retrieve BL32's bootargs from bl32_ep_info ...

This patch removes the bootargs pointer from the platform params
structure. Instead the bootargs are passed by the BL2 in the
bl32_ep_info struct which is a part of the EL3 params struct.

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

Move dispatcher documents to the docs/spd folder ...

This patch moves the optee-dispatcher.md and tlk-dispatcher.md to
docs/spd.

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