Use 'units' value instead of guessing based on integer/FP

We still end up guessing based on magnitude of the value, though: it
might be 'bar' or 'mbar', we end up picking one or the other based on
just how big the value is.

I should make it look at any possible explicit units too, since at least
with good xml, they exist.  Of course, the only good xml I've seen so
far is the one we generate ourselves ;)

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>