gpg: Allow generating Ed25519 key from an existing key.
* g10/misc.c (map_pk_gcry_to_openpgp): Add EdDSA mapping.
Due to this missing mapping a "gpg --export --full-gen-key" with
selection "13 - Existing key" did not worked for an ed25519 key.
(cherry picked from commit 346a98fabe03adf2e202e36fc2aa24b1c2571154)
- Signed-off-by: Werner Koch <email@example.com>