ppc/pnv: add phb-id/chip-id PnvPHB4RootBus properties

The same rationale provided in the PHB3 bus case applies here.

Note: we could have merged both buses in a single object, like we did
with the root ports, and spare some boilerplate. The reason we opted to
preserve both buses objects is twofold:

- there's not user side advantage in doing so. Unifying the root ports
presents a clear user QOL change when we enable user created devices back.
The buses objects, aside from having a different QOM name, is transparent
to the user;

- we leave a door opened in case we want to increase the root port limit
for phb4/5 later on without having to deal with phb3 code.

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>
Message-Id: <20220811163950.578927-3-danielhb413@gmail.com>

include/hw/pci-host/pnv_phb4.h

@@ -45,7 +45,17 @@ typedef struct PnvPhb4DMASpace {
     QLIST_ENTRY(PnvPhb4DMASpace) list;
 } PnvPhb4DMASpace;
 
+/*
+ * PHB4 PCIe Root Bus
+ */
 #define TYPE_PNV_PHB4_ROOT_BUS "pnv-phb4-root"
+struct PnvPHB4RootBus {
+    PCIBus parent;
+
+    uint32_t chip_id;
+    uint32_t phb_id;
+};
+OBJECT_DECLARE_SIMPLE_TYPE(PnvPHB4RootBus, PNV_PHB4_ROOT_BUS)
 
 /*
  * PHB4 PCIe Host Bridge for PowerNV machines (POWER9)