Fix xae(4) driver attachement on the Government Furnished Equipment (GFE)
riscv cores.

GFE cores come with standard DTS file that lacks standard 'dmas ='
property, which means xae(4) could not find a DMA controller to use.

The 'dmas' property could not be added to the DTS file because the
ethernet controller and DMA engine parts in Linux are implemented
in a single driver.

Instead of 'dmas' property the standard Xilinx 'axistream-connected'
property is provided, so fallback to use it instead.

Suggested by: James Clarke <jrtc27@jrtc27.com>
Reviewed by: James Clarke <jrtc27@jrtc27.com>
Sponsored by: DARPA, AFRL