ARM: dts: imx6: Add support for phyBOARD-Mira with i.MX 6QuadPlus

Add support for the PHYTEC phyBOARD-Mira with i.MX 6QuadPlus with NAND.
It is based on the phyBOARD-Mira with i.MX 6Quad/Dual and supports the
same interfaces.

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Signed-off-by: Stefan Lengfeld <s.lengfeld@phytec.de>
Signed-off-by: Christian Hemp <c.hemp@phytec.de>
Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>