ASoC: rsnd: remove unnecessary ADG flags

The flag LRCLK_ASYNC / AUDIO_OUT_48 had been added to handling
special case of Salvator-X board, but it is not used on upstream.
It makes code complex today, let's remove these.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87zg9y5emm.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>