mpc85xx: Add support for the MPC8536DS reference board

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Srikanth Srinivasan <srikanth.srinivasan@freescale.com>
Signed-off-by: Dejan Minic <minic@freescale.com>
Signed-off-by: Jason Jin <Jason.jin@freescale.com>
Signed-off-by: Dave Liu <daveliu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>