PCI: hv: Reorganize the code in preparation of hibernation

There is no functional change. This is just preparatory for a later
patch which adds the hibernation support for the pci-hyperv driver.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>