pci: Add defines for normal and subtractive PCI bridges

Add following two new PCI class codes defines into pci_ids.h include file:

  PCI_CLASS_BRIDGE_PCI_NORMAL
  PCI_CLASS_BRIDGE_PCI_SUBTRACTIVE

And use these defines in all U-Boot code for describing PCI class codes for
normal and subtractive PCI bridges.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>