mips: MIPSCPU model subclasses

mips: MIPSCPU model subclasses

Register separate QOM types for each mips cpu model,
so it would be possible to reuse generic CPU creation
routines.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[PMD: use internal.h, use void* to hold cpu_def in MIPSCPUClass,
 mark MIPSCPU abstract, address Eduardo Habkost review]
Tested-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Yongbok Kim <yongbok.kim@imgtec.com>