[POWERPC] Add the MPC8641 HPCN platform files.

Signed-off-by: Xianghua Xiao <x.xiao@freescale.com>
Signed-off-by: Haiying Wang <Haiying.Wang@freescale.com>
Signed-off-by: Wei Zhang <Wei.Zhang@freescale.com>
Signed-off-by: Jon Loeliger <jdl@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>