ARM: dts: imx6q-icore-rqs: Update model to support Dual SOM

Engicam i.CoreM6 Dual and Quad SOM's use same dts file, hence
update model name to add Dual and also added full mode decsription.

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>