ASoC: tegra+wm8903: remove non-DT support for Seaboard

In kernel 3.6, Seaboard will only be supported when booting using device
tree; the board files are being removed. Hence, remove the non-DT support
for Seaboard and derivatives Kaen and Aebl from the audio driver.

Harmony is the only remaining board supported by this driver when not
using DT. This support is currently scheduled for removal in 3.7.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>