[POWERPC] 86xx: Add aliases node to 8641hpcn DTS file.

The addition of the aliases node is needed for U-Boot
and, eventually, cuImage, to help locate the proper
nodes reliably when using the libfdt approach.

Signed-off-by: Jon Loeliger <jdl@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>