ARM: add basic support for Trusted Foundations

Trusted Foundations is a TrustZone-based secure monitor for ARM that
can be invoked using the same SMC-based API on supported platforms.
This patch adds initial basic support for Trusted Foundations using
the ARM firmware API. Current features are limited to the ability to
boot secondary processors.

Note: The API followed by Trusted Foundations does *not* follow the SMC
calling conventions. It has nothing to do with PSCI neither and is only
relevant to devices that use Trusted Foundations (like most Tegra-based
retail devices).

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>