test: dm: pci: Add tests for mixed static and dynamic devices on the same bus

In the Sandbox test configuration, PCI bus#0 only has static devices
while bus#1 only has dynamic devices. Create a bus#2 that has both
types of devices and test such.

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