dt-bindings: fsl-imx-sdma: Add i.MX8MM/i.MX8MN/i.MX8MP compatible string

Add imx8mm/imx8mn/imx8mp sdma support.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1578893602-14395-1-git-send-email-Anson.Huang@nxp.com


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