We sometimes permit omitting the first option name, for example
-device foo is short for -device driver=foo.  The name to use
("driver" in the example) is passed as argument to qemu_opts_parse().
For each QemuOptsList, we use at most one such name.

Move the name into QemuOptsList, and pass whether to permit the
abbreviation.  This ensures continued consistency, and simplifies the
commit after next in this series.