pci: include pci_internal.h inside pci_auto.c

To avoid a build warning with W=1, provide a function prototype for
dm_pciauto_prescan_setup_bridge, which is a non-static function whose
definition is inside pci_auto.c.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>