minicircuits gain ctrl testbench added

minicircuits gain ctrl hdl added as RFFE submodules
swap RF channels hdl added as RFFE submodule

I have accidentally commited changes made into
the submodule hdl/ip_cores/general-cores. That
created a unpublished commit that was unable to
reach. Now, the submodule points to a valid commit
and no longer references the original project,
but a fork from it hosted in github.

hdl/testbench/wishbone/wb_fmc150_test/verilog: cleanup generated simulation files

modules/custom_wishbone/wb_fmc150: extra support for simulation