ASoC: rt5645: move RT5645 muxes to rt5645_specific_dapm_widgets

This is a similar patch to "move RT5650 muxes to rt5650_specific_
dapm_widgets" patch. The purpose is to silence the "has no paths"
warnings.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>