dt-bindings: net: xlnx,axi-ethernet: Introduce DMA support

Xilinx 1G/2.5G Ethernet Subsystem provides 32-bit AXI4-Stream buses to
move transmit and receive Ethernet data to and from the subsystem.

These buses are designed to be used with an AXI Direct Memory Access(DMA)
IP or AXI Multichannel Direct Memory Access (MCDMA) IP core, AXI4-Stream
Data FIFO, or any other custom logic in any supported device.

Primary high-speed DMA data movement between system memory and stream
target is through the AXI4 Read Master to AXI4 memory-mapped to stream
(MM2S) Master, and AXI stream to memory-mapped (S2MM) Slave to AXI4
Write Master. AXI DMA/MCDMA enables channel of data movement on both
MM2S and S2MM paths in scatter/gather mode.

AXI DMA has two channels where as MCDMA has 16 Tx and 16 Rx channels.
To uniquely identify each channel use 'chan' suffix. Depending on the
usecase AXI ethernet driver can request any combination of multichannel
DMA channels using generic dmas, dma-names properties.

Example:
dma-names = tx_chan0, rx_chan0, tx_chan1, rx_chan1;

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/1700074613-1977070-2-git-send-email-radhey.shyam.pandey@amd.com


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