ASoC: sh: Drop SUPERH platform dependency

The SIU sound peripheral is used only on SuperH SH-Mobile platforms.
As both SUPERH and ARCH_SHMOBILE are set for these platforms, the SUPERH
dependency can be dropped.

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