Add extra CPU model flags to some CPU models when the full CPU model
can't be tested easily.

Note that the code loads the reference files using the CPU flags as part
of the file name too (so we can be sure we're reading the right dump
file)  This way we can be sure we are comparing the output of "-cpu
Foo,-flag" against a dump that was surely generated using "-cpu
Foo,-flag" as well (not just "-cpu Foo").
Signed-off-by: NEduardo Habkost <ehabkost@raisama.net>