ASoC: rt5640: move DAC2 Power to rt5640_dapm_widgets

"DAC L2 Power" and "DAC R2 Power" are used by both rt5639 and rt5640.
But it was defined in rt5640_specific_dapm_widgets[]. Move them to
rt5640_dapm_widgets will let both rt5639 and rt5640 can use it.

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