[POWERPC] 85xx: SBC8548 - Add flash support and HW Rev reporting

The following adds local bus, flash and MTD partition nodes for
sbc8548. As well, a compatible field for the soc node, so that
of_platform_bus_probe() will pick it up.

Something that is provided through this newly added epld node
is the Hardware Revision which is now being utilized.

Signed-off-by: Jeremy McNicoll <jeremy.mcnicoll@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>