ASoC: amd: vangogh: Centralize strings definition

Replace occurrences of strings by their definition, avoiding
bugs where the string changed, but not all places have been modified.
While at it rename defines to use NAU8821 codec name instead of NUVOTON
and align with the other defines.

Signed-off-by: Lucas Tanure <lucas.tanure@collabora.com>
Link: https://lore.kernel.org/r/20230217110850.1045250-9-lucas.tanure@collabora.com


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