ARM: dts: sun8i: Orange Pi Plus dts is for the Plus and Plus 2

Update the sun8i-h3-orangepi-plus.dts model string to reflect that it
is valid for both the Orange Pi Plus and the Orange Pi Plus 2.

This is also meant to help users realize that it is not valid for
the new Orange Pi Plus 2E, which will get its own dts.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>