powerpc/44x: Add AMCC Arches eval board support

The Arches Evaluation board is based on the AMCC 460GT SoC chip.
This board is a dual processor board with each processor providing
independent resources for Rapid IO, Gigabit Ethernet, and serial
communications.  Each 460GT has it's own 512MB DDR2 memory, 32MB NOR FLASH,
UART, EEPROM and temperature sensor, along with a shared debug port.
The two 460GT's will communicate with each other via shared memory,
Gigabit Ethernet and x1 PCI-Express.

Signed-off-by: Victor Gallardo <vgallardo@amcc.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>