Attest: Add a SP to support test to get IAK public key

Add a test service to support tests to get Initial Attestation public
key.
In some cases, Initial Attestation public key can only be read in
runtime. This test service provides an interface for tests to read the
public key to verify the IAT in tests.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I6f910f9f05becbf1e2e56d1fd421ea013fc885e2
9 files changed