arm64: dts: allwinner: add 'chassis-type' property

A new 'chassis-type' root node property has recently been approved for
the device-tree specification, in order to provide a simple way for
userspace to detect the device form factor and adjust their behavior
accordingly.

This patch fills in this property for end-user devices (such as laptops,
smartphones and tablets) based on Allwinner ARM64 processors.

Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20211016102025.23346-2-arnaud.ferraris@collabora.com