We're going to need more state while processing a list of repeated
options. This change eliminates "repeated_opts_first" and adds a new state
variable:
Additionally, it is documented that lookup_scalar() and processed(), both
called by opts_type_XXX(), are invalid in LM_STARTED -- generated qapi
code calls opts_next_list() to allocate the very first link before trying
to parse a scalar into it. List mode restrictions are expressed in
positive / inclusive form.