ASoC: soc-core: add asoc_rtd_to_cpu/codec() macro

ASoC: soc-core: add asoc_rtd_to_cpu/codec() macro

Now, snd_soc_pcm_runtime supports multi cpu_dai/codec_dai.
It still has cpu_dai/codec_dai for single DAI,
and has cpu_dais/codec_dais for multi DAIs.

	dais  = [][][][][][][][][][][][][][][][][][]
		^cpu_dais         ^codec_dais
		|--- num_cpus ---|--- num_codecs --|

	/* for multi DAIs */
	rtd->cpu_dais   = &rtd->dais[0];
	rtd->codec_dais = &rtd->dais[dai_link->num_cpus];

	/* for single DAI */
	rtd->cpu_dai    = rtd->cpu_dais[0];
	rtd->codec_dai	= rtd->codec_dais[0];

But, these can be replaced by dais.
This patch adds asoc_rtd_to_cpu() / asoc_rtd_to_codec() macro for it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/875zevk5va.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>