dt-bindings: fsl-qdma: Add NXP Layerscpae qDMA controller bindings

Document the devicetree bindings for NXP Layerscape qDMA controller
which could be found on NXP QorIQ Layerscape SoCs.

Signed-off-by: Wen He <wen.he_1@nxp.com>
Signed-off-by: Peng Ma <peng.ma@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>