ohci: QOM'ify some more

Introduce type constant and avoid DO_UPCAST().

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
[AF: Avoid remaining OHCIPCIState::pci_dev uses, rename parent fields]
Signed-off-by: Andreas Färber <afaerber@suse.de>
ohci: Use QOM realize for OHCI

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>