ASoC: soc.h: use array instead of playback/capture_widget

snd_soc_pcm_runtime has playback/capture_widget for Codec2Coddec.
The naming is unclear.
This patch names it as c2c_widget and uses array.

	struct snd_soc_pcm_runtime {
		...
=>		struct snd_soc_dapm_widget *playback_widget;
=>		struct snd_soc_dapm_widget *capture_widget;
		...
	}

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87pmfqv9mk.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>