bus/pci: support MMIO for ioport

bus/pci: support MMIO for ioport

With I/O BAR, we get PIO (port-mapped I/O) address.
With MMIO (memory-mapped I/O) BAR, we get mapped virtual address.
We distinguish PIO and MMIO by their address range like how kernel does,
i.e, address below 64K is PIO.
ioread/write8/16/32 is provided to access PIO/MMIO.
By the way, for virtio on arch other than x86, BAR flag indicates PIO
but is mapped.

Signed-off-by: Huawei Xie <huawei.xhw@alibaba-inc.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Tested-by: Yinan Wang <yinan.wang@intel.com>