[POWERPC] 83xx: Add base support for the MPC8313E RDB

Add support for the MPC8313E Reference Development Board (RDB).  The board
is a mini-ITX reference board with 128M DDR2, 8M flash, 32M NAND, USB, PCI,
gigabit ethernet, and serial.

Signed-off-by: Wilson Lo <Wilson.Lo@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>