pci: sandbox: Support dynamically binding device driver

At present all emulated sandbox pci devices must be present in the
device tree in order to be used. The real world pci uclass driver
supports pci device driver matching, and we should add such support
on sandbox too.

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