dt-bindings: gpu: mali-utgard: Add compatible for A64 Mali

Allwinner A64 has Mali-400MP2, so document the relevant compatible
as "allwinner,sun50i-a64-mali" along with reset line.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>