Use 16-channel virtual mux on Cosmo #2154
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labbott
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nathanaelhuffman
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Right now, the Cosmo FPGAs (main and front) both pretend to contain a set of PCA9545 muxes. This PR switches to a single virtual 16-channel mux, which reduces writes (since we no longer need to deactivate virtual mux N before activating virtual mux M).
Having a single mux also makes it more logically consistent to have a single reset pin, see https://github.com/oxidecomputer/hardware-cosmo/issues/619
Finally, it gives us a place to put the delay required by the physical switches' timing that doesn't mess with our existing driver.
So far, this PR only has Hubris changes; FPGA updates to come.