Convert atse(4) driver for Altera Triple-Speed Ethernet MegaCore to use
xdma(4) interface.
This allows us to switch between Altera mSGDMA or SoftDMA engines used by
atse(4) device.
This also makes atse(4) driver become 25% smaller.
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9618