Add DDR options setting on MPC8641HPCN board

* Add board specific parameter table to choose correct cpo, clk_adjust,
write_data_delay based on board ddr frequency and n_ranks.

* Set odt_rd_cfg and odt_wr_cfg based on the dimm# and CS#.

Signed-off-by: James Yang <James.Yang@freescale.com>
Signed-off-by: Haiying Wang <Haiying.Wang@freescale.com>