ANDROID: PCI: Add backport reserved field to struct pci_host_bridge.

Keep open the possibility of backporting the patch
https://lore.kernel.org/linux-pci/20250715-pci-port-reset-v6-1-6f9cce94e7bb@oss.qualcomm.com/


after KMI thaw window closed.

Bug: 416734898
Bug: 438087210
Change-Id: I4421d553140fdbf85833cc1f122e7269923d6b16
Signed-off-by: Tsai Sung-Fu <danielsftsai@google.com>