ASoC: soc-pcm: makes snd_soc_dpcm_can_be_xxx() local function

Hi Mark

No driver is calling snd_soc_dpcm_can_be_xxx() functions. We don't need to have EXPORT_SYMBOL_GPL() for them. This patch-set makes it static function.

Thank you for your help !!

Best regards --- Kuninori Morimoto