dt-bindings: dmaengine: sifive,fu540-c000: include generic schema

Include generic dma-controller.yaml schema, which enforces node naming
and other generic properties.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220318162044.169350-1-krzysztof.kozlowski@canonical.com