pci: Add CONFIG_PCI_SKIP_HOST_BRIDGE config option

In current source code, when the device number of PCI is 0, process PCI
bridge without fail. However, when the device number is 0, it is not PCI
always bridge. There are times when device of PCI allocates.

When CONFIG_PCI_SKIP_HOST_BRIDGE is enable, this problem is solved when
use this patch.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Acked-by: Stefan Roese <sr@denx.de>