scd: Add very basic support for PIV cards.
* scd/app-piv.c: New. * scd/Makefile.am (card_apps): Add app-piv.c * scd/app.c (app_new_register): Try to get a Yubikey serial number. Detect the PIV application. (get_supported_applications): Add "piv".
Right now this allows the use of the authentication key (9A) for SSH
authentication. More support will follow soon.
Tested with Yubikey-5.