scd:p15: Allow signing for CVISION cards

* scd/app-p15.c (do_sign): Add code for Starcos 3.2 and the CVISION
product.

The code for the Starcos cards has been implemented according to the
3.52 manual However, this does not work with my test cards. Protocol
analysis shows that decryption can be used for the cryptovision
product. Thus we do it the same for now.