OvmfPkg/PvScsiDxe: Backup/Restore PCI attributes on Init/UnInit

This commit doesn't change semantics.
It is done as a preparation for future commits which will modify
PCI attributes.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2567
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Message-Id: <20200328200100.60786-10-liran.alon@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>

OvmfPkg/PvScsiDxe/PvScsi.h

@@ -20,6 +20,7 @@
 typedef struct {
   UINT32                          Signature;
   EFI_PCI_IO_PROTOCOL             *PciIo;
+  UINT64                          OriginalPciAttributes;
   UINT8                           MaxTarget;
   UINT8                           MaxLun;
   EFI_EXT_SCSI_PASS_THRU_PROTOCOL PassThru;