scd:p15: Detect CardOS 5 cards and print some basic infos.

* scd/app-p15.c (read_ef_odf): Detect the home_DF on the fly.  Silence
the garbage warning for null bytes.
(print_tokeninfo_tokenflags): New.
(read_ef_tokeninfo): Print manufacturer, label, and flags.
(app_select_p15): No need to use the app_get_slot macro.
(CARD_TYPE_CARDOS_50): New const.
(card_atr_list): Detect CardOS 5.0

The card under test is a "Test-Signaturkarte D-TRUST Card 3.1" for a
mere 49 Euro and no specs available. D-Trust is a branch of the
German Bundesdruckerei. Compare that to Telesec and Yubikey who have
always been nice enough to send bunches of sample cards without a need
to wade through lots of forms and not even asking for money. Guess
which cards I prefer.

(backported from master)

• Signed-off-by: Werner Koch <wk@gnupg.org>