PCI: hv: Decouple the func definition in hv_dr_state from VSP message

hv_dr_state is used to find present PCI devices on the bus. The structure
reuses struct pci_function_description from VSP message to describe a
device.

To prepare support for pci_function_description v2, decouple this
dependence in hv_dr_state so it can work with both v1 and v2 VSP messages.

There is no functionality change.

Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>