dump: Move HMP command handlers to dump/

dump: Move HMP command handlers to dump/

Move the HMP handlers related to qapi/dump.json to
dump/dump-hmp-cmds.c, where they are covered by MAINTAINERS section
"Dump", just like qapi/dump.json.

Cc: Marc-André Lureau <[email protected]>
Cc: "Dr. David Alan Gilbert" <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>
Message-Id: <20190619201050[email protected]>
Reviewed-by: Daniel P. Berrangé <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
[Commit message typo fixed]