ASoC: Add compatible strings for JZ4760(B) SoC

Add the ingenic,jz4760b-codec and ingenic,jz4760-codec compatible
strings.

In the process, convert the previous compatible strings to use an enum
instead.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20210123140958.12895-1-paul@crapouillou.net
Signed-off-by: Mark Brown <broonie@kernel.org>