ASoC: meson: g12a: extract codec-to-codec utils

The hdmi routing mechanism used on g12a hdmi is also used:
* other Amlogic SoC types
* for the internal DAC path

Each of these codec glues are slightly different but the idea
behind it remains the same. This change extract some helper functions
from the g12a-tohdmitx driver to make them available for other Amlogic
codecs.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200213155159.3235792-3-jbrunet@baylibre.com


Signed-off-by: Mark Brown <broonie@kernel.org>