ASoC: rsnd: Remove obsolete platform data support

Since commit 3d7608e4 ("ARM: shmobile: bockw: remove legacy
board file and config"), Renesas R-Car SoCs are only supported in
generic DT-only ARM multi-platform builds.  The driver doesn't need to
use platform data anymore, hence remove platform data configuration.

Move <sound/rcar_snd.h> to sound/soc/sh/rcar/, as it's no longer needed
by platform code.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>