ASoC: Intel: byt-rt5640: Update internal mic and speaker kcontrol names

Use more sensible kcontrol names than "Int Mic" and "Ext Spk". Speakers
especially are usually integrated devices in sales models.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Liam Girdwoood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>