ASoC: rsnd: cleanup RSND_REG_xxx

SRC Gen1 support was removed. Current rsnd driver is sharing Gen1/Gen2
register index to reduce memory, but there is no effect anymore.
Let's remove share definition and merge RSND_REG_xxx

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>