Add driver for Xilinx XDMA PCIe Bridge found in the U.S. Government
Furnished Equipment (GFE) riscv cores.

GFE cores are synthesized on the Xilinx Virtex UltraScale+ FPGA VCU118
Evaluation Kit.

Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D23337