reset PMBA and PMREGMISC PIIX4 registers.

The bug causes Windows + OVMF hang after reboot since OVMF
checks PMREGMISC to see if IO space is enabled and skip
configuration if it is.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>