powerpc/85xx: Optimized DDR settings for 800MT/s on P1/P2 RDB

Changed the following DDR timing parameters for 800Mt/s:
tRRT    BL/2+1 to  BL/2
tWWT    BL/2+1 to  BL/2
tWRT    BL/2+1 to  BL/2
tRWT    BL/2+1 to  BL/2
REFINT  6500ns to  7800ns

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>