dt-bindings: net: sun4i-emac: add dma support

The sun4i EMAC supports DMA for data transmission,
so it is necessary to add DMA options to the device tree bindings.

Signed-off-by: Conley Lee <conleylee@foxmail.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/tencent_4E434174E9D516431365413D1B8047C6BB06@qq.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>