powerpc/mpc8xxx: Fix DDR3 timing_cfg_1 and sdram_mode registers

The write recovery time of both registers should match. Since mode register
doesn't support cycles of 9,11,13,15, we should use next higher number for
both registers.

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