x86: qemu: Convert to use DM PCI API

Use pci_[read|write]_config intead of x86_pci_[read|write]_config.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>