ARM: sunxi: Add machine match for the Allwinner V3 SoC

The Allwinner V3 SoC shares the same base as the V3s but comes with
extra pins and features available. As a result, it has its dedicated
compatible string (already used in device trees), which is added here.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201031182137.1879521-2-contact@paulk.fr