arm64: dts: imx8mp-beacon-kit: Enable WM8962 Audio CODEC

The baseboard has an WM8962 Audio CODEC connected to the SAI3
peripheral.  The CODEC supports stereo in and out
and a microphone input connected to the headphone jack.
Route this CODEC through the simple-audio-card driver.

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