target-i386: Add range check for -cpu ,family=x

A family field value of 0xf and extended family field value of 0xff is
the maximum representable unsigned family number.
All other CPUID property values are bounds-checked, so add a check here
for symmetry before we adopt it in a property setter.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
