[POWERPC] 86xx: Add localbus and flash nodes to mpc8641_hpcn.dts

Add local bus, flash, and MTD partition nodes to mpc8641_hpcn.dts

Also add compatible field for the soc node, so that it will be picked up
by of_platform_bus_probe().

Signed-off-by: Wade Farnsworth <wfarnsworth@mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>