ASoC: simple-amplifier: add VCC regulator widget

Amplifier may have assosicated regulator, so add a widget for it
and appropriate route.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>