gpg: Allow generating Ed25519 key from an existing key.

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.

Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit 346a98fabe03adf2e202e36fc2aa24b1c2571154)
(cherry picked from commit 31d2a1eecaee766919b18bc42b918d9168f601f8)

Gbp-Pq: Topic from-2.2.13
Gbp-Pq: Name gpg-Allow-generating-Ed25519-key-from-an-existing-key.patch