[flash_loader] Implement Flash Loader via PCIe/Wishbone

[lerwys]

Problem: A long standing issue is remote programing of the FPGA. Currently we use a JTAG cable to program the FPGA directly (serial) or in flash. This is bad, as we need to ahve a physical cable connected to the board.

Solution: Implement a flash loader module to program FPGA flash through PCIe/Wishbone.

O good start would be here:
http:https://www.ohwr.org/projects/svec/repository/revisions/master/show/hdl/rtl/bootloader