Attest: Crypto service binding

Refactor initial attestation key handling and replace
crypto stub functions with calls to Crypto service to
sign properly the initial attestation token.

Change-Id: I1cdd331769b0e631d08e96f8d15a2f5a59a51a1e
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
12 files changed