scd: Disable pinpad if it's impossible by KDF DO.
* scd/app-openpgp.c (struct app_local_s): Add pinpad.disabled field. (do_getattr): Set pinpad.disabled field. (check_pinpad_request): Use the pinpad.disabled field. (do_setattr): Update pinpad.disabled field.
- GnuPG-bug-id: T4832
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>