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

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

No driver is calling snd_soc_dpcm_can_be_xxx() functions. We don't need
to have EXPORT_SYMBOL_GPL() for them. Let's makes it static function.
One note is that snd_soc_dpcm_fe_can_update() is not used in upstream.
Use #if-endif and keep it for future support.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://patch.msgid.link/87h6b6df7e.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>