powerpc/85xx: Board support for ppa8548

Initial board support for the Prodrive PPA8548 AMC module. Board
is an MPC8548 AMC platform used in RapidIO systems. This module is
also used to test/work on mainline linux RapidIO software.

PPA8548 overview:
- 1.3 GHz Freescale PowerQUICC III MPC8548 processor
- 1 GB DDR2 @ 266 MHz
- 8 MB NOR flash
- Serial RapidIO 1.2
- 1 x 10/100/1000 BASE-T front ethernet
- 1 x 1000 BASE-BX ethernet on AMC connector

Signed-off-by: Stef van Os <stef.van.os@prodrive.nl>
Acked-by: Timur Tabi <timur@tabi.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>