sound: Move Samsung-specific code into its own file

The i2s code is in fact Samsung-specific, but there might be other
implementation. Move this code into its own file. This makes it slightly
more obviously how to adjust the code to support another SoC, when someone
takes this task on.

Also drop non-FDT support, since it isn't used on Exynos 5.

Tested-by: Che-Liang Chiou <clchiou@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>