qemu: command: wire up usage of q35/ich9 disable s3/s4
    
    If the q35 specific disable s3/s4 setting isn't supported, fallback to
    specifying the PIIX setting, which is the previous behavior. It doesn't
    have any effect, but qemu will just warn about it rather than error:
    
      qemu-system-x86_64: Warning: global PIIX4_PM.disable_s3=1 not used
      qemu-system-x86_64: Warning: global PIIX4_PM.disable_s4=1 not used
    
    Since it doesn't error, I don't think we should either, since there
    may be configs in the wild that already have q35 + disable_s3/4 (via
    virt-manager)