bus/pci: support hot-unplug handler

bus/pci: support hot-unplug handler

This patch implements the ops to handle hot-unplug on the PCI bus.
For UIO PCI, it could avoids BARs read/write errors by creating a
new dummy memory to remap the memory where the failure is. For VFIO
or other kernel driver, it could specific implement function to handle
hot-unplug case by case.

Signed-off-by: Jeff Guo <jia.guo@intel.com>
Acked-by: Shaopeng He <shaopeng.he@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>