machine: use class base init generated name

machine: use class base init generated name

machine_class_base_init() member name is allocated by
machine_class_base_init(), but not freed by
machine_class_finalize().  Simply freeing there doesn't work,
because DEFINE_PC_MACHINE() overwrites it with a literal string.

Fix DEFINE_PC_MACHINE() not to overwrite it, and add the missing
free to machine_class_finalize().

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>