hw/misc has collected a few things that could be moved elsewhere.

Move two ADC devices into the adc directory.

Create a sensor directory and move the sensors into it.  There's only a
few for now, but the people driving the BMC work are going to be adding
many more, and it would really clutter up hw/misc.  This is the main
reason for the patch set.

I was unable to run the tests to completion, but I think I ran the ones
that matter.  The end of master fails the BIOS tests for i386, at least,
and it hangs the test run.  I backed out these changes and
double-checked.

-corey