MLK-25654: dts: arm: imx7d sdb: medium quality sound example

Add device tree to enable meidum quality sound support
for iMX7D SabreSD, MQS_L/MQS_R pins on J20.

Signed-off-by: Adrian Alonso <adrian.alonso@nxp.com>
Reviewed-by: Shengjiu Wang <shengjiu.wang@nxp.com>