Added firmware support for adc_mux to handle swapping I/Q, etc.

Added firmware support for adc_mux to handle swapping I/Q, etc.
Modified dsp_core_rx.v to swap A and B mapping so that the software
thinks that the TVRX is connected to A/D A.

ISE 10.1 SP3 is required to compile the FPGA successfully.  SP2 is
insufficient.  It compiles with SP2, but the firmware doesn't load.
Only the F led is one in that case.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@9795 221aa14e-8319-0410-a670-987f0aec2ac5