mips hw/: Don't use CPUState

Scripted conversion:
  for file in hw/mips_*.[hc]; do
    sed -i "s/CPUState/CPUMIPSState/g" $file
  done

Signed-off-by: Andreas Färber <afaerber@suse.de>
Acked-by: Anthony Liguori <aliguori@us.ibm.com>