powerpc/85xx: Add support for MPC8536DS

Add support for the MPC8536 process and MPC8536DS reference board.  The
MPC8536 is an e500v2 based SoC which eTSEC, USB, SATA, PCI, and PCIe.

The USB and SATA IP blocks are similiar to those on the PQ2 Pro SoCs and
thus use the same drivers.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>