powerpc/86xx: Basic flash support for GE SBC610

Support for the SBC610 VPX Single Board Computer from GE (PowerPC MPC8641D).

This patch adds basic support for the on-board flash.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>