hv: vPCI: cache PCI BAR physical base address

PCI BAR physical base address will never changed. Cache it to avoid calculating
it every time when we access it.

Tracked-On: #3475
Signed-off-by: Li, Fei1 <fei1.li@intel.com>
Acked-by: Eddie Dong <eddie.dong@Intel.com>

hypervisor/include/hw/pci.h

@@ -185,6 +185,7 @@ struct pci_bar {
 	/* Base Address Register */
 	union pci_bar_reg reg;
 	uint64_t size;
+	uint64_t base_hpa;
 	bool is_64bit_high; /* true if this is the upper 32-bit of a 64-bit bar */
 };