dm: pci: Allow scan bridge child devices before relocation

On some platforms pci devices behind bridge need to be probed (eg:
a pci uart on recent x86 chipset) before relocation. Remove such
limitation so that dm pci can be used before relocation.

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