maintainer-pgp-guide: update ECC support information

Update ECC sections with the latest details, now that Yubikeys are able
to support ED25519 curves. Tweak a few links to smartcard devices to
reflect the latest URL changes.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220727-docs-pgp-guide-v2-3-e3e6954affb6@linuxfoundation.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>