ASoC: meson: g12a-toacodec: use regmap fields to prepare SM1 support

Switch usage to regmap field for bits handled by the g12a_toacodec_mux_put_enum()
function to avoid uselesss code duplication when adding SM1 variant support.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20210511074829.4110036-2-narmstrong@baylibre.com


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