DPE: Optimise dpe initialisation and RoT derivation

Optimise dpe initialisation and RoT context derivation such that:
* Under both test and non-test flow, use actual derived RoT CDI.
* Under both test and non-test flow, avoid export-import of RoT CDI key.
* Also on partition init do not call psa_destroy_key as there is no key.

Signed-off-by: Maulik Patel <maulik.patel@arm.com>
Change-Id: I830dd22b54db896ac471c61aac526abb84598266
3 files changed