[v2,7/9] dmaengine: pxa_dma: use dmaenginem_async_device_register to simplify the code

Huang Shijie [off-list ref] writes:

Use dmaenginem_async_device_register to simplify the code:
	remove dma_async_device_unregister.

Signed-off-by: Huang Shijie <redacted>

Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>