ASoC: sunxi: sun50i-codec-analog: Add support for cpvdd regulator supply

On the Allwinner A64 SoCs, the audio codec has a built-in headphone
amplifier. This amplifier has a power supply separate from the rest of
the analog audio circuitry, labeled cpvdd.

This patch adds a DAPM widget for this supply, and ties it to the
headphone amp widget.

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>