ASoC: rockchip: Add machine driver for RK3288 boards that use analog/HDMI

The driver is used for Rockchip rk3288-based boards using a configurable
analog output (can be an headphone) and the built-in HDMI audio output
that is part of the RK3288 SoCs and use the Alsa HDMI codec driver. For
some rk3288-based boards the analog output and the hdmi audio are plugged
on the same i2s line, so we have to do the same in the driver by using a
DAI link CPU to multicodecs. This configuration can be found for example
on the Radxa Rock2 or the Firefly-RK3288.

This commit is based on the initial work that was done by Sjoerd Simons
<sjoerd.simons@collabora.com> with some improvements.

Signed-off-by: Romain Perier <romain.perier@collabora.com>
Signed-off-by: Mark Brown <broonie@kernel.org>