ARM: dts: sun4i: Add support for Topwise A721 tablet

The Topwise A721/LY-F1 tablet is a tablet sold around 2012 under
different brands. The mainboard mentions A721 clearly, so this tablet
is best known under this name.

Signed-off-by: Pascal Roeleven <dev@pascalroeleven.nl>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210224105240.47754-3-dev@pascalroeleven.nl