feat(tc): add DPE backend to the measured boot framework

The client platform relies on the DICE attestation
scheme. RSS provides the DICE Protection Environment
(DPE) service. TF-A measured boot framework supports
multiple backends. A given platform always enables
the corresponding backend which is required by the
attestation scheme.

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Change-Id: Idc3360d0d7216e4859e99b5db3d377407e0aeee5
8 files changed