arm64: dts: allwinner: a64: enable sound on Pinebook

The Pinebook has a headphone jack tied to the HP headphone output of
the SoC, and internal speakers connected to the LINEOUT of the SoC,
through a standalone amplifier.

This commit enables I2S, digital and analog parts of audio codec on
Pinebook, along with a device node for the external amplifier.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
[wens@csie.org: dropped headphone_amp; added headphone amp regulator supply;
		fixed speaker_amp node name and sound-name-prefix name]
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Tested-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>