ASoC: rsnd: add .get_id/.get_id_sub

ID for CTU and SSIU are confusable.
1 CTU has 4 sub nodes. This means, CTU0 has CTU01 - CTU03, CTU1 has
CTU10 - CTU13. SSIU is more confusable. Gen2 SSIU has BUSIF0-3, Gen3
SSIU has BUSIF0-7, but not for all SSIU.
In rsnd driver, each mod drivers are assuming rsnd_mod_id() returns
main device ID (In CTU case CTU0-1, SSIU case SSIU0-9), not serial
number.
This patch adds new .id/.id_sub to handling more detail ID.

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