[POWERPC] 4xx: Add AMCC Canyonlands 460EX eval board support to platforms/44x

Canyonlands is the AMCC 460EX eval board, featuring nearly all of the 460EX
interfaces:

- 1 * PCI (max 66MHz), 2 * PCIe (one 4-lane, one 1-lane)
- 2 * GBit Ethernet with TCP/IP acceleration
- USB 2.0 Host/Device OTG and Host interface
- SATA port

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>