i386: Register feature bit properties as class properties

i386: Register feature bit properties as class properties

Class properties make QOM introspection simpler and easier, as
they don't require an object to be instantiated.

Also, the hundreds of instance properties were having an impact
on QMP commands that create temporary CPU objects.  On my
machine, run time of qmp_query_cpu_definitions() changed
from ~200ms to ~16ms after applying this patch.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20201111183823.283752-5-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>