qapi: add a dictionary form with 'name' key for enum members

qapi: add a dictionary form with 'name' key for enum members

Desugar the enum NAME form to { 'name': NAME }. This will allow to add
new enum members, such as 'if' in the following patch.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20181213123724.4866-7-marcandre.lureau@redhat.com>
Message-Id: <20181213123724.4866-8-marcandre.lureau@redhat.com>
Message-Id: <20181213123724.4866-9-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Harmless accidental move backed out, long line wrapped, patches
squashed]
Signed-off-by: Markus Armbruster <armbru@redhat.com>