ARM: dts: imx6qdl-icore: Add Sound card support

Linux Sound card now uses generic simple-audio-card, so add
the same along with related audmux and codec(via u2c3) for
i.CoreM6 QDL module boards.

Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>