[POWERPC] Add 8548 CDS PCI express controller node and PCI-X device node

Add 8548 CDS PCI express controller node and PCI-X device node. The current
dts file is suitable for 8548 Rev 2.0 board with Arcadia 3.1.

This kind of board combination is the most popular.

Used the following compatible properties:
	PCI	"fsl,mpc8540-pci"
	PCI-X:	"fsl,mpc8540-pcix"
	PCIe:	"fsl,mpc8548-pcie"

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>