dmaengine: imx-sdma: add a test for imx8mq multi sdma devices

On i.mx8mq, there are two sdma instances, and the common dma framework
will get a channel dynamically from any available sdma instance whether
it's the first sdma device or the second sdma device. Some IPs like
SAI only work with sdma2 not sdma1. To make sure the sdma channel is from
the correct sdma device, use the node pointer to match.

Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>