arm64: dts: imx8mm-beacon: Migrate sound card to simple-audio-card

Instead of using a custom glue layer connecting the wm8962 CODEC
to the SAI3 sound-dai, migrate the sound card to simple-audio-card.
This also brings this board in line with the imx8mn-beacon and
imx8mp-beacon.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>