ASoC: dapm: Unexport snd_soc_dapm_new_control()

Everything now uses snd_soc_dapm_new_controls() instead so we don't need
to make it part of the external API.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>