tegra: fdt: Add EMC data for Tegra2 Seaboard

This adds timings for T20 and T25 Seaboards, using the bindings found here:

http://patchwork.ozlabs.org/patch/132928/



We supply both full speed options for normal running, and half speed options
for testing / development.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>