ARM: dts: rockchip: add missing model properties

ARM: dts: rockchip: add missing model properties

A test with the command below gives these errors:

arch/arm/boot/dts/rk3288-evb-act8846.dt.yaml: /: 'model'
is a required property
arch/arm/boot/dts/rk3288-evb-rk808.dt.yaml: /: 'model'
is a required property
arch/arm/boot/dts/rk3288-r89.dt.yaml: /: 'model'
is a required property

Fix this error by adding the missing model properties to
the involved dts files.

make ARCH=arm dtbs_check
DT_SCHEMA_FILES=~/.local/lib/python3.5/site-packages/dtschema/
schemas/root-node.yaml

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20200304074051.8742-1-jbx6244@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>