dt-bindings: net: cdns,macb: allow dma-noncoherent

commit 2c3eba8436253162f527960a5d7aa2e0d866fa6b from
https://github.com/linux4microchip/linux.git

 linux-6.1-mchp+fpga

PolarFire SoC may be configured in a way that requires non-coherent DMA
handling. On RISC-V, buses are coherent by default & the dma-noncoherent
property is required to denote buses or devices that are non-coherent.

Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Saravanan.K.S <saravanan.kadambathursubramaniyam@windriver.com>