pci: Tidy up PCI host bridges

Adopt the QOM parent field name and enforce QOM-style access via casts.
Don't just typedef PCIHostState, either use it directly or embed it.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/hw/spapr_pci.h b/hw/spapr_pci.h
index 4140ee6..670dc62 100644
--- a/hw/spapr_pci.h
+++ b/hw/spapr_pci.h
@@ -35,7 +35,7 @@
     OBJECT_CHECK(sPAPRPHBState, (obj), TYPE_SPAPR_PCI_HOST_BRIDGE)
 
 typedef struct sPAPRPHBState {
-    PCIHostState host_state;
+    PCIHostState parent_obj;
 
     uint64_t buid;
     char *busname;