powerpc/corenet_ds: Use separated speed tables for UDIMM and RDIMM

RDIMM has different timing parameters from UDIMM. Create new tables for
RDIMMs. Single-, dual- and quad-rank RDIMMs have been verified with speeds
from 800 to 1333MT/s. Speed table expands to include 1600MT/s for future
use. Single- and quad-rank RDIMM entries are copied into UDIMM tables for
future use.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>