xen/pvhvm: Remove the xen_platform_pci int.

Since we have  xen_has_pv_devices,xen_has_pv_disk_devices,
xen_has_pv_nic_devices, and xen_has_pv_and_legacy_disk_devices
to figure out the different 'unplug' behaviors - lets
use those instead of this single int.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>