vDPA/ifcvf: make use of virtio pci modern IO helpers in ifcvf

This commit discards ifcvf_ioreadX()/writeX(), use virtio pci
modern IO helpers instead

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Link: https://lore.kernel.org/r/20220222115428.998334-2-lingshan.zhu@intel.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>