dmaengine: remove zte zx driver

The zte zx platform is getting removed, so this driver is no
longer needed.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jun Nie <jun.nie@linaro.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Link: https://lore.kernel.org/r/20210120131859.2056308-3-arnd@kernel.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>