ARM: omap4: Update sdram setting for panda rev A6

OMAP4 panda rev A6 is a 4430 es2.3 IC with an updated memory
part.

The panda rev A6 uses Elpida 2x4Gb memory and no longer uses Micron
so the timings needs to be updated

Signed-off-by: Dan Murphy <dmurphy@ti.com>