ARM: dts: imx6qdl-tqma6: Add partitions subnode to spi-nor

ARM: dts: imx6qdl-tqma6: Add partitions subnode to spi-nor

The bootloader may add MTD partitions in this subnode if present.
Add an empty partitions node which the bootloader will fill with
configured MTD partitions. Remove #size-cells from MTD node
because this is deprecated.

Signed-off-by: Markus Niebel <Markus.Niebel@ew.tq-group.com>
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>