ARM: dts: imx6dlq-wandboard-revb1.dts: use unique model id

Downstream packages like Debian flash-kernel use
/proc/device-tree/model
to determine which dtb file to install.

Hence each dts in the Linux kernel should provide a unique model
identifier.

Commit 8536239e ("ARM: dts: Restructure imx6qdl-wandboard.dtsi for new
rev C1 board.")' created new files imx6dl-wandboard-revb1.dts and
imx6q-wandboard-revb1.dts but used the same model identifier as in
imx6dl-wandboard.dts and imx6q-wandboard.dts.

This patch provides unique model identifiers for revision B1 of
the Wandboard Dual and Wandbaord Quad.

The patch leaves imx6dl-wandboard.dts and imx6q-wandboard.dts unchanged
because it is not foreseeable if the same dts will valid for future
board revisions or not. Furthermore we should avoid unnecessary
changes.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>