MAINTAINERS: Match on allwinner keyword

Some drivers (phy, crypto, net) folders don't have sunxi in it but
allwinner. Add that keyword to match on it too.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Jernej Skrabec <jernej.skrabec@siol.net>
Link: https://lore.kernel.org/r/20210331130830.64182-2-maxime@cerno.tech