feat(fconf): support signing-key in root cert node

Until now we have only supported describing chain of trusts through the
CoT DTB with a single ROTPK so the signing key for root certificates was
implicit. Therefore signing key was not a supported property in the
root certificates node.

Now we want to extend that to describe CoTs with mulitiple roots of
trust so we need a way to specify for each root certificate with which
ROTPK it should be verified. For that, we reuse the 'signing-key'
property already in use for the non-root certificates, but we make it
optional for root certificates in single-RoT CoTs and for root
certificates signed with the default ROTPK in multi-RoT CoTs.

Change-Id: I41eb6579e8f1d01eaf10480fe5e224d2eed9c736
Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
1 file changed