ddb: use _FLAGS command macros where appropriate
Some command definitions were forced to use DB_FUNC in order to specify
their required flags, CS_OWN or CS_MORE. Use the new macros to simplify
these.
Reviewed by: markj, jhb
MFC after: 3 days
Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D35582