dm: pci: Use a 1:1 mapping for bus <-> phy addresses

If U-Boot gets used as coreboot payload all pci resources got
assigned by coreboot. If a dts without any pci ranges gets used
the dm is not able to access pci device memory. To get things
working make use of a 1:1 mapping for bus <-> phy addresses.

This change makes it possible to get the e1000 U-Boot driver
working on a sandybridge device where U-Boot is used as coreboot
payload.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: fixed 'u-boot' in the commit message]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>