ARM: dts: tqma6ul: Add partitions subnode to spi-nor

ARM: dts: tqma6ul: Add partitions subnode to spi-nor

The bootloader adds MTD partitions in this subnode if present, or in the
spi-nor node itself otherwise.
Setting #size-cells in MTD nodes itself is deprecated by mtd.yaml.
Fix all this by adding an empty partitions node which the bootloader will
fill with configured MTD partitions. Remove the deprecated properties
as well.

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>