Add attestation key management

Adds component to manage access and creation of the IAK.  Allows
for factory provisioned and generate-on-first-run strategies.
Extended the attestation reporter tests to use the key manager
to allow the signed report to be verified.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I01e126a8a18a7b3d24a0b322885aa9e558070250
16 files changed