This adds a simple wishbone mux. The idea is that each slave gets its
own address bit. This lends itself to extemely simple address decoding,
but uses up address space quickly. In theory, we could also give larger
addres space to some slaves, but currently lower bits have priority. The
testbench is also very simple. Since everything is combinatorial, we can
determine the outputs from the inputs exactly.
Signed-off-by: Sean Anderson <seanga2@gmail.com>
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