Add Synchronous Audio Interface(SAI) node for Engicam GEAM6UL
and Is.IoT MX6UL variant module boards.

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