pci: iproc: Set all 24 bits of PCI class code

pci: iproc: Set all 24 bits of PCI class code

Register 0x43c in its low 24 bits contains PCI class code.

Update code to set all 24 bits of PCI class code and not only upper 16 bits
of PCI class code.

Use standard U-Boot macro (PCI_CLASS_BRIDGE_PCI << 8) for constructing all
24-bits of PCI class for PCI bridge Normal decode.

Signed-off-by: Pali Rohár <pali@kernel.org>
Acked-by: Roman Bacik <roman.bacik@broadcom.com>